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Class 8th-Science: Chapter 7-Conservation of Plants and Animals

” Why Conservation of plants and animals is important?”

Conservation of plants and animals is important because their conservation helps to build a heal thy ecosystem and it is necessary to maintain natural balance so plants and animals are very essintial for well-being and survival of mankind.

7.1 Deforestation and its causes

Deforestation means cutting of forests and using that land for other purposes.

Causes of Deforestation are:-

(i) Land for cultivation.

(ii) Building houses and factories.

(iii) Making furnitures from wood.

Some natural causes of Deforestation are:-

(i) forest fires.

(ii) severe Droughts

7.2 Consequence of Deforestation

Deforestation has many harmful consequences:-

(i) It increases temperature of earth.

(ii) increases pollution level.

(iii) increases level of CO2 in atmosphere.

(iv) Due to it level of ground water gets lowered.

(v) Many useful medicinal plants get vanished with Deforestation.

(vi) Rainfall Decreases.

(vii) Furtility of soil Decreases.

(viii) Chances of floods and droughts increases.


It is the slow process of conversion of furtile land into Desert.

Desertification increases due to Deforestation because properties of soil like nutrient content, texture of soil etc. Changes due to Deforestation.

7.3 Conservation of Forest and Wildlife

To protect forests and wildlife some protected areas are made by government. These protected areas are wildlife sanctuaries, national parka and biosphere reserves etc.

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Class 8th-Science: Chapter 6-Combustion and flame


In general Definition:

A process of burning something is known as combustion.

In science:

A chemical process in which a substance reacts with oxygen to give off heat is callled combustion.

Examples of Combustion:

(i) Burning of magnesium ribbon

Mg + O2 —> MgO + Heat + light

(ii) Burning of Coal

C + O2 —> CO2 + Heat + light


The hot, glowing and visible part of a fire is known as flame.


Any combustible substance that produces heat (sometime light also) after combustion is known as fuel.

Example of fuel:

Coal, Charcoal, petrol, diesel, wood, CNG(Compressed Natural Gas), LPG(Liquified Petroleum Gas) etc.

“Types of substance on the bases of Combustible:-“

(i) Combustible

A combustible substance is that substance which can burn in air.


Coal, wood, paper etc.

(ii) Non Combustible

A non-combustible substance is that which cannot burn in air.


Iron, glass, gold, etc.

Table 6.1

Necessary condition under which combustion can take place:

(i) presence of oxygen.

(ii) presence of combustible substance.

(iii) Ignition temperature.

Let us discuss above 3 conditions one by one:-

(i) presence of oxygen:-

from the above activity we can see that without air (oxygen) candle flame goes off.

=> oxygen is required for combustion.

(ii) presence of combustible substance:-

for combustion a combustible substance is required because a incombustible substance cannot burn even if there is lot of oxygen.

(iii) Ignition temperature:-

The lowest temperature at which a substance catches fire is known as ignition temperature.

Different materials have different ignition temperature.

For Example:-

A paper catches fire as soon as a burning matchstic is brought near it because it has low ignition temp.

But a piece of wood do not catches fire as soon as we bring a burning matchstick it take a lot time also we use paper of kerosene oil to start fire in wood because wood has higher ignition temperature.

Inflammable substances: the substances which have very low ignition temperature and can easily eatch fire with a flame, are called inflammable substances.

6.2 How Do We Control Fire?

We know following are three essential requirements for producing fire

(i) air (to supply oxygen)

(ii) Fuel (Combustible substance)

(iii) ignition temperature or (heat to raise the temperature above ignition temperature)


“Fire can be controlled by removing one or more of these above requirements.”

so fire can be extinguished in 3 ways:-

(i) By cutting off air supply to burning substance.

(ii) By removing fuel(combustible substance)

(iii) By removing heat, so that temp can be lowered down below ignition temperature

Fire Extinguisher:

Anything that can be used to control or stop fire is known as Fire Extinguisher.

For Example: (i) water, (ii) CO2 Carbondioxide atc.


Water is the most common fire extinguisher.

” How water controls fire “

water can control fire because

(i) it has a coding effect

(ii) water makes a layer between burning substance and air (oxygen) this layer acts as a barrier between burning substance and oxygen.


(i) water is not suitable for Fires involving oil and petrol because water is havier than oil it sinks below the oil keeps burning on top.

(ii) it is also not suitable for Fire on electrical equipment because water can conduct electricity.

6.3 Types of Combustion

Combustion can be classified into three main types

(i) Rapid combustion

(ii) Spontaneous combustion

(iii) Explosion

(i) Rapid combustion:-

The combustion in which a substance burns rapidly and produces heat and light is known as rapid combustion.

for example:

(i) When we bring burning lighter near a gas stone it burns rapidly and gives heat and light.

(ii) The burning of kerosene oil in kerosene stone.

(ii) Spontaneous combustion:

The type of combustion in which a material suddenly burst into flames, without the application of any apparent cause is called spontaneous combustion.

For Example

(i) Burning of phosphorus at room temp.

(ii) Spontaneous combustion of coal dust.

(iii) some forest fires are spontaneous due to heat of the sun.

(iii) Explosion:

A very fast combustion in which a large amount of heat, light and sound are produced is known as explosion or explosive combustion.


Fireworks which we explode during Diwali etc.

6.4 Flame

The hot glowing and visible part of a fire is known as flame.

We know that:- colours of candle flame and LPG flame is different but why?

Different flames give diff colours because complete combustion gives blue flame and partial combustion gives yellow flame.

LPG requires less oxygen as compaired to candle that why LPG burns completly in environment but for candle environmentle oxygen is not sufficient and it burns partially.

why some substances give flame while burning and some not.

The substances which vapourise during burning give flame.

Examples: kerosene oil, molten wax etc.

The substance which do not vapourise do not give flame.

different zones of candle flame:

6.6 What is a fuel:

Any combustible substance that produces heat (sometimes light also) after combustion i known as fuel.

For Example:

Coal, wood, charcoal, petrol, diesel, LPG, CNG etc.

Characteriatics of good fuel:-

A good fuel is that which have following properties

(i) It should be easily available.

(ii) It should be cheap.

(iii) It burns easily in air at moderate rate.

(iv) It produces a large amount of heat(high calorific value).

(v) produces less pollution.

(vi) its storage and transportation is easy.

6.7 Fuel Efficiency:

Fuel efficiency will be greater if its calorific value is high.

Calorific value:

The amount of heat energy produced on complete combustion of 1 Kg of fuel is called calorific value.

It is expressed in kilojoule per Kg (KJ/Kg)

Harmful Effects of Burning of fuel:-

(i) unburnt carbon particle can cause respiratory diseases like “Asthma”.

(ii) Incomplete combustion of carbon fuels gives carbon monoxide gas. Which is very poisonous gas.

(iii) Carbondioxide produced during combustion is a major cause of global warming.

(iv) Burning Coal and diexel releases sulphur dioxide (SO2) gas. Which is suffocating as.

Also petrol engines give off oxides of nitrogen oxides of sulphur and nitrogen dissolve in rain water and form acid such rain is called acid rain.

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Class 8th-Science: Chapter 1-Crop Production and Management Ncert

Q1.   Select the correct word from the following list and fill in the blanks.

(a)   The same kind of plants grown and cultivated on a large scale at a place is called ________.

(b)   The first step before growing crops is ________ of the soil.

(c)   Damaged seeds would ________ on top of water.

(d)   For growing a crop. suffcient sunlight and _________ and ________ from the soil are essentila.

Ans. (a) Crop  (b)  preparation  (c)  float  (d)  water ,nutrients

Q2.   Match items in column A with those in column B.

                              A                                B
(i)  Kharif crops(a)  Food for cattle
(ii)  Rabi crops(b)  Urea and super phosphate 
(iii)  Chemical fertilisers(c)  Animal excreta. cow dung urine and plant waste
(iv)  Organic manure(d)  Wheat, gram, pea
(e)  Paddy and malze

Ans.  (i)(e), (ii)(d), (iii)(b), (iv)(c)

Q3.   Give two examples of each.

    (a) Kharif crop

    (b) Rabi crop

Ans.   (a)  Two examples of kharif crops are (i) Padddy (ii) Maize

           (b)   Two example of Rabi crops are (i) Wheat (ii) Gram

Q4.   Write a paragraph in your own words on each of the following.

    (a)  Preparation of soil

    (b)  Sowing

    (c)  Weeding

    (d)  Threshing

Ans.   (a)  It is the first step of growing crops in, this generally soil is turned and loosened.

    Activities that prepare soil are ploughing, watering and sometime manure is also added.

          (b)  Sowing is the process of planting seeds on prepared soil.

               for food production of crop it is necessary to have seeds of good quality because they are more immune to diseases and can produce healthy plants, so selection of seeds becomes important in sowing.

         (c)   Weeds are the unwanted plants that grow along with the crop.

   The removal of weeds is called weeding.

   We remove weeds because they compete with the crop plants for water, nutrients, space, sunlight etc. thus they affect the growth of crop, even some weeds may be poisonous for animals and humans.

 (d)  The process of separating seeds from the chaff is called threshing, it can done either by manual or with the help of machine.

Q5.   Explain how fertilisers are different from manure.


        Fertilisers Manure 
(i)  Fertilisers are the chemicals which are rich in aparticular nutrient.(i)  Manure is an organic substance obtained from the decomposition of plant or animal waste.
(ii)  Fertilisers are prepared in factories.(ii) Can be prepared in fields.
(iii)  Do not provide humus.(iii)  Provide humus.
(iv)  Very rich in nutrients.(iv)  Relatively less rich in nutrients. 
(v)  Example are urea, ammonium sulphate etc.(v)  Example cow dung.

 Q6.   What is irrigation? Describe two mettods of irrigation which conserve water.

Ans.   The supply of water to crops at regular intervals is called irrigation.

Two mwthods of irrigation which conserve water are

(i)  Sprinkler method:  In this method of irrigation perpendicular pipes with rotating nozzles on top are joined to main pipeline at regular interval, when water comes out from rotating nozzles it gets sprinkled on crop as if it is raining.

(ii)   Drip irrigation:  Inthis system water falls drop by drop directly near the roots, thats why it is called drop irrigation.

Q7.   If wheat is sown in the Kharif season. what would happen? Discuss.

Ans.   We know wheat is a Rabi crop and it requires cold climate to grow, so if it is sown in Kharif season then complete crop would be destroyed due to unsuitable conditions.

Q8.   Explain how soil gets affected hy the continuous plantation of crops in a field.

Ans.   We know soil provide nutrients to crop so continuous plantation of same crop in a field makes soil poorer in certain nutrients, so soil can become infertile after sometime.

Q9.   What are weeda? How can we control them?

Ans.   Weeds are the unwanted plants that grow along with the crop.

We can control them

(i)   By using weedicides: weedicides are chemicals that can kill the weeds without klling crop plant.

(ii)   By removing them: The removal of weeds is called weeding.

Q10.   Arrange the following boxes in proper order to make a flow chart of sugarcane crop production.

Sending crop to sugar factory, Irrigation, Harvesting, Sowing, Preparation of soil, Ploughing the field,Manuring

Ans.   Preparation of soil —-> Ploughing the field —> Sowing —> Manuring —> Irrigation —> Harvesting —> Sending crop to sugar factory

Q11.  Complete the following word puzzle with the help of clues given below.


1. Providing water to the crops.

2. Keeping crop grains for a long time nuder proper conditions.

5. Certain plants of the same kind grown on a large scale.


3. A machine used for cutting the matured crop.

4. A rabi crop that is also one of the pulses.

6. A process of separating the grain from chaff.

Ans.   1. Irrigation

          2. Storage

          3. Harvester

          4. Gram

          5. Crop

          6. Winnowing

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Class 8th-Science: Chapter 2-Microorganisms: Friend and Foe Ncert

Q1.  Fill in the blanks.

        (a)  Microorganisms can be seen with the help of a _________.

        (b)  Blue green algae fix _________ directly from air and enhance fertilit of  soil.

        (c)  Alcohol is produced with the help of ________.

        (d)  Cholera is caused by _________.

Ans.  (a) microscope, (b) Nitrogen gas, (c) yeast, (d) Bacteria

Q2.  Tick the correct answer.

        (a)  Yeast is used tn the production of

               (i)  sugar

               (ii) alcohol

               (iii) hydrochloric acid

               (iv) oxygen

        (b)  The following is an antibiotic

               (i) Sodium bicarbonate

               (ii) Streptomycin

               (iii) Alcohol

               (iv) Yeast

        (c)  Carrier of malaria-causing protozoan is

                (i) female Anopheles mosquito

               (ii) cockroach

               (iii) housefly

               (iv) butterfly

        (d)  The most common carrier of communicable diseases is

               (i) ant

               (ii) housefly

               (iii) dragongly

               (iv) spider

        (e)  The bread or idli dough rises because of 

               (i) heat

               (ii) grinding

               (iii) growth of yeast cells

               (iv) kneading

        (f)   The process of conversion of sugar into alcohol is called

               (i) nitrogen fixation

               (ii) moulding

               (iii) fermentation

               (iv) infection

Ans. (a) (ii), (b) (i), (c) (i), (d) (ii), (e) (iii), (f) (iii)

Q3.  Match the organisms in Column A with their action in Column B.

                        A                          B
(i) Bacteria(a) Fixing nitrogen
(ii) Rhizobium(b) Setting of curd
(iii) Lactobacillus(c) Baking of bread
(iv) Yeast(d) Causing malaria
(v) A protozoan(e) Causing cholera
(vi) A virus(f) Causing AIDS
(g) Producing antibodies

Ans.  (i) (e), (ii) (a), (iii) (b), (iv) (c), (v) (d), (vi) (f)

 Q4.  Can microorganisms be seen with the naked eye? If not, how can they be  seen?

Ans.  No, we can not see microorganisms with naked eye. They can be seen with the help microscope.

Q5.  What are the major groups of microorganisms?

Ans.  The major groups of microorganisms are bacteria, fungi, protozoa and some algae.

Q6.  Name the microorganisms which can fix atmospheric nitrogen in the soil.

Ans.  Rhizobium, some bacteria and blue green algae can fix atmospheric nitrogen in the soil.

Q7.  Write 10 lines on the usefulness of microorganisms in our lives.

Ans. The usefulness of microorganisms is as follows:

  1. Lactobacillus, a bacterium is useful in the formation of curd.
  2. Yeast is used in the baking industry for making breads, pastries and cakes.
  3. Yeast is also used for the commerical production of alcohol and wine.
  4. Microorganisms like bacteria and fungi are used to make antibiotics. Examples of these antibiotics are streptomycin, tetracycline and erythromycin.
  5. Antibiotics are mixed with the feed of livestock and poultry to check microbial infection in animals.
  6. Antibiotics are also used to cantrol many plant diseases.
  7. Microorganisms are also used to make vaccines.
  8. They are used to degrade the harmful and smelly substances and thereby clean up the environment.
  9. They are used to make manures.
  10. Some bacteria and blue green algae can fix nitrogen from atmosphere to enrich soil with nitrogen and increase fertility.

 Q8.  Write a short paragraph on the harmful effects of microorganisms.

Ans.  Some of the microorganisms causes diseases in human beings, plants and  animals. Some microorganisms also spoil food, clothing and leather. Many communicable diseases such as cholera, common cold, chicken pox,                    tuberculosis etc. are caused by microorganisms. Protozoans cause serious diseases like dysentery and malaria. Female Anopheles mosquito carries the parasite of malaria. Female Aedes mosquito acts as carrier of dengue virus.        Anthrax is a dangerous human and cattle disease caused by a bacterium. Foot and mouth disease of cattle is caused by a virus. Several microorganisms cause diseases in plants like wheat, rice, potato, sugarcane, orange, apple and        other. The diseases reduce the yield of crops. Food poisoning is also caused by microorganisms. They make food poisonous by producing toxic substances in it.      

Q9.  What are ntibiotics? What precautions must be taken while taking antibiotics?

Ans. Antibiotics:

        The medicines that kill or stop the growth of the disease-causing microorganisms are called antibiotics.

        Examples of some antibiotics that are made from bacteria and fungi are streptomycin, tetracycline and erythromycin. 

        The precautions that can be taken while taking antibiotics are as follows:

  1.  These medicines should be taken only on the advice of a qualified doctor.
  2.  One must complete the course prescribed by the doctor.
  3.  If antibiotics are taken when not needed or in wrong does, it may make the drug less effective when it might be needed in future.
  4. Also antibiotics taken unnecessarily may kill the beneficial bacteria in the body.
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Class 8th-Science: Chapter 3-Synthetic Fibers and Plastics Ncert

Q1.  Explain why some fibres are called synthetic.

Ans.  The synthetic fibres are made by human beings. That is why these are called synthetic or man-made fibres. Some examples of synthetic fibres are rayon, nylon, poiyester, acrylic, etc.

Q2.  Mark the correct answer.

      (a) it has a silk-like appearance.

      (b) it is obtained from wood pulp.

      (c) its fibres can also be woven like those of natural fibres.

Ans.  (b) it is obtained from wood pulp.

Q3.  Fill in the blanks with appropriate words.

      (a) Synthetic fibres are also called ________ or _______ fibres.

      (b) Synthetic fibres are synthesised from raw material called ________.

      (c) Like synthetic fibres plastic is also a _________.

Ans.  (a) man-made, artificial

         (b) petro-chemicals

         (c) polymer

Q4.  Give examples which indicate that nylon fibres are very strong.

Ans.  Nylon fibers are very strong, elastic and light that’s why they are used for making parachutes and ropes for rock climbing. It is scientifically tested that a nylon thread is stronger than a steel wire. 

Q5.  Explain why plastic containers are favoured for storing food.

Ans.  Plastic containers are favoured for storing food because of the following reasons:

1. They have light weight.

2. They are easy to handle.

3. They have good strengh.

4. They are generally cheaper than metals.

5. They are durable.

Q6.  Explain the difference between thermoplastic and thermosetting plastics.

Ans.  Thermoplastics

1. The plastic which gets deformed easily on heating and can be bent easily are known as thermoplastics.

2. For Example: Polythene, PVC

3. They are used for manufacturing toys, combs and various types of containers.

Thermosetting plastics

1. Those plastics which when moulded once, can not be softened by heating are called thermosetting plastics.

2. For Example: Bakelite and Melamine

3. Bakelite

(i) Bakelite is a poor conductor of heat and electricity.

(ii) It is used for making electrical switches, handles of various utensils and screw drivers etc.


(i) Melamine is a versatile material. It resists fire and can tolerate heat better than other plastics.

(ii) It is used for making floor tiles, kitchenware and fabrics which resist fire.

Q7.  Explain why the following are made of thermosetting plastics.

      (a) Saucepan handles

      (b) Electric plugs/switches/plug boards

Ans.  (a) Thermosetting plastics are used to make saucepan handles because they are bad conductors of heat and also on heating, these plastics do not get softened.

         (b) Bakelite is a kind of thermosetting plastic which is a bad conductor of heat and electricity. Because of this property it is used for making electric plugs, switches, plug boards, etc.

Q8.  Categorise the materials of the following products into ‘can be recycled’ and ‘cannot be recycled’.

Telephone instruments, plastic toys, cooker handles, carry bags, ball point pens, plastic bowls, plastic covering on electrical wires, plastic chairs, electrical switches.

Ans.  Can be Recycled: Plastic toys, Carry bags, Bail point pens, Plastic bowls, Plastic covering on electrical wires, Plastic chairs.

         Cannot be Recycled: Telephone instruments, Cooker handles, Electrical Switches.

Q9.  Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason.

Ans.  Rana should buy cotton shirts for summer. Because cotton absorbs the sweat coming out of the body and the pores in cotton allows easy evaporstion and keeps our body cool. Whereas synthetic shirts don’t absorb sweat, so they are very uncomfortable to wear in summers. 

Q10.  Give examples to show that plastics are noncorrosive in nature.

Ans.  Plastics are non-corrosive in nature. They do not react with water, air and the materials contained in it. That is why they are used to store various kinds of material, including many chemicals.

For example:

1. The cleaning chemicals that we use at home are stored in plastic bottles, instead of metal containers.

2. Many containers like bucket, mug, water bottles. Food containers are made by using plastics.

Q11.  Should the handle and bristles of a tooth brush be made of the same material? Explain your answer.

Ans.  The handle and bristle of a tooth brush should be made of different material because The handles of brushes should be made of hard material so that it can give a strong grip, but bristle of a tooth brush should be made of soft material so that is does not harm the gums. 

Q12.  ‘Avoid plastics as far as possible’. Comment on this advice.

Ans.  We should avoid plastics as far aas possible due to the following reasons:

1. Since plastic is non-biodegradable, because it takes several years to decompose, it is not environment friendly. It causes enviromental pollution. 

2. Besided, the burning process in the synthetic material is quite slow and it does not get completely burnt easily. In the process it releases lots of poisonous fumes into the atmosphere causing air pollution.

3. Sometimes cows and other animals may eat plastics present in the gaebage which may choke their respiratory system and even cause death.

4. Plastic bage drained in the water bodies cause threat to that aquatic life also.

5. The polybags carelessly thrown here and there are responsible for clogging the drains and sewage pipes thus causing lot of trouble.

Q13.  Match the terms of column A correctly with the phrases given in column B.

          A                                    B
(i) Polyester(a) Prepared by using wood pulp
(ii) Teflon(b) Used for making parachutes and stockings
(iii) Rayon(c) Used to make non-stick cookwares
(iv) Nylon(d) Fabrics do not wrinkle easily

Ans.  (i) (d), (ii) (c), (iii) (a), (iv) (b)

Q14.  /Manufacturing synthetic fibres is actually helping conservation of forests’. Comment.

Ans.  The synthetic fibres are man-made fibres. They are made up of petrochemicals. So. Manufacturing synthetic fibres does not depend upon plants or animals. These synthetic fibres fulfill the need of people upto great extent. Thus, the forests are not destroyed to manufacture clothes and other items. So, indirectly, we can come to a conclusion that manufacturing synthetic fibres is actually helping conservation of forests.

Q15.  Describe an activity to show to show that thermoplastic is a poor conductor of electricity. 

Ans.  If we make an experimental set up using copper wire, a thermoplastic object, a bulb and a battery, as shown in the figure, the bulb does not glow.

However, if the thermoplastic object is removed from the circuit, the bulb glows up. This shows that thermoplastics are bad conductor of electricity.   

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Class 8th-Science: Chapter 5- Coal and Petroleum Ncert

Q1.  What are the advantages of using CNG and LPG as fuels?

Ans.  The advantages of using CNG and LPG as fuels are as follows:

  1. These are less polluting and cleaner fuels.
  2. They give a lot of heat energy when burnt.
  3. Both are easy to store and transport.
  4. They are easily available and have affordable cost.
  5. They can be used directly for burning in homes and factories where they can be supplied through pipes.

Q2.  Name the petroleum product used for surfacing of roads.

Ans.  Bitumen, which is a petroleum product, is used for surfacing of roads.

Q3.  Describe how coal is formed from dead vegetation. What is this process called?

Ans.  About 300 million years ago the earth had dense forests in low lying wetland areas. Due to natural processes, like flooding, these forests got buried under the soil. As more soil deposited over them, they were compressed. The temperature also rose as they sank deeper and deeper. Under high pressure and high temperature, dead plants got slowly converted to coal.

Q4.  Fill in the blanks.

       (a)  Fossil fuels are ________, ________ ans __________.

       (b)  Process of separation of different constituents from petroleum is called                  _______.

       (c)  Least polluting fuel for vehicle is ________.

Ans.  (a)  Coal, petroleum, natural gas

         (b)  refining

         (c)  CNG(Compressed Natural Gas)

Q5.  Tick True/False against the following statements.

       (a)  Fossil fuels can be made in the laboratory.

       (b)  CNG is more polluting fuel than petrol.

       (c)  Coke is almost pure form of carbon.

       (d)  Coal tar is a mixture of various substances.

       (f)  Kerosene is not a fossil fuel.

Ans.  (a) False, (b) False, (c) True, (d) True, (e) False

Q6.  Explain why fossil fuele are exhaustible natural resources.

Ans.  Coal, petroleum and natural gas are fossil fuels. It required the dead organisms millions of years to get converted into these fuels. On the other hand, the known reserves of these will last atmost a few hundred years. So, if these are exhausted by human activities, cannot be recreated in a short period of time, that’s why fossil fuels are exhaustible natural resources. 

Q7.  Describe characteristics and uses of coke.  

Ans. Characterictics of coke:

  1. Coke is porous
  2. It is tough
  3. It is a black substance and 
  4. It is almost pure form of carbon.

​​​​​​​         Uses of coke:

  1. Coke is used in the manufacture of steel and 
  2. It is also used in the extraction of many metals.

Q8.  Explain the process of formation of petroleum.

Ans.Petroleum was formed from organisms living in the sea. As these organisms died, their bodies settled at the bottom of the sea and got covered with layers of sand and clay. Over millions of years, absence of air, high temperature and high pressure transformed the dead organisms into petroleum and natural gas.

Q9.  The following Table shows the total power shortage in India from 1991-1997. Show the data in the form of a graph. Plot shortage percentage for the years on the Y-axis and the year on the X-axis.


​​​​​Scale: X-axis:2 units = 1 year

           Y-axis: 2 units = 1%

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Class 8th-Science: Chapter 6- Combustion and Flame Ncert

Q1.  List conditions under which combustion can take place.

Ans. Necessary Conditions for Combustion are:-

(1) Presence of air to supply oxygen.

(2) Presence of Combustible Substance.

(3) Heat to achive ignition temoerature.

Q2.  Fill in the blanks.

        (a) Burning of wood and coal causes __________ of air.

        (b) A liquid fuel, used in homes is ____________.

        (c) Fuel must be heated to its _________, ________ before it starts burning.

        (d) Fire produced by oil cannot be controlled by _________.

Ans. (a) Pollution (b) Kerosene oil or LPG (c) Ignition, temperature (d) water

Q3.  Explain how the used of CNG in automobiles has reduced pollution in our cities.

Ans. CNG in automobiles has reduced pollution in our cities because.

(1) It gives very less amount of harmful gases like carbon dioxide, Carbon monoxide, Sulphur dioxide etc.

(2) It burns Completly without leaving any unburnt substance that’s why it is considered as cleaner fuel.

Q4.  Compare LPG and wood as fuels.

Ans. LPG

(1) LPG produces very less pollution.

(2) Calorific value is very high.

(3) Leaves no residue.

(4) Easy to store and transport.


(1) Wood produces more pollution.

(2) low calorific value.

(3) Leaves ash as residue.

(4) not easy to store and transport as required more space.

Q5.  Give reasons.

        (a) Water is not used to control fires involving electrical equipment.

        (b) LPG is a better domestic fuel than wood.

        (c) Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.

Ans. (a) Water is not used to control fires involving electrical equipment because water in its impure form can conduct electricity and can cause harm to people.

(b) LPG is better domestic fuel than wood because,

(i) It has high calorific value.

(ii) Creates very less pollution.

(iii) No smoke is produced.

(iv) Storage and transportation is easy.

(v) LPG can instantly catch fire but it take time to start burning of wood

(c) Paper by itself catches fire easily because it has low ignition temoerature, but when this paper is wrapped around an aluminium pipe, heat given to paper is absorbed by aluminium pipe and it take time to reach I.T.

Q6.  Make a labelled diagram of a candie flame.

Q7.  Name the unit in which the calorific value of a fuel is expressed.

Ans. Kilojoule per Kg (KJ/Kg)

Q8.  Explain how CO2 is able to control fires.

Ans. CO2 is havier than oxygen, it forms a blanket around fire and stopes the oxygen supply, and we know without oxygen substance cannot burn.

Q9.  It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.

Ans. Heap of green leaves contains a lot of water in it that’s why their ignition temperature is high and they are difficult to burn.

but Dry leaves have no water and that’s why they have low ignition temperature can burn easily.

Q10.  Which zone of a flame does a goldsmith use for melting gold and silver and why?

Ans. Goldsmith uses outermost zone of a flame because it is the hottest zone of a flame.

Q11.  In an experiment 4.5 kg of a fuel was completely burnt. The heat produced was measured to be 180.000 kj. Calculate the calorific value of the fuel.

Ans. Colorific value = Heat produced in KJ/ mass of fuel in Kg

= 180,000 KJ/4.5 Kg

= 18,00,000/45 KJ/Kg

= 40000 KJ/Kg

Q12.  Can the process of rusting be called combustion? Discuss.

Ans. No, rusting cannot be called combustion because.

(1) Combustion requires ignition temperature but rusting do not requires ignition temperature.

(2) rusting is very slow process as compaired to combustion.

Q13.  Abida and Ramesh were doing an experiment in which water was to be heated in a beaker. Abida kept the beaker near the wick in the yellow part of the candle flame. Ramesh kept the beaker in the outermost part of the flame. Whose water will get heated in a shorter time?

Ans. Water of Ramesh’s beaker will get heated in shorter time because outermost part of the flame is hottest part.

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Class 8th- Science: Chapter 4-Materials: Metals and Non-Metals Ncert

Q1. Which of the following can be beaten into thin sheets?

(a) Zinc

(b) Phosphorus

(c) Sulphur

(d) Oxygen

Ans. (a) Zinc

Q2. Which of the following statements is correct?

(a) All metals are ductile.

(b) All non-metals are ductile.

(c) Generally, metals are ductile.

(d) Some non-metals are ductile.

Ans. (c) Generally, metals are ductile.

Q3. fill in the blanks:

(a) Phosphorus is very ________ non-metals.

(b) Metals are _________ conductors of heat and _________.

(c) Iron is _________ reactive than copper.

(d) Metals react with acids to produce _________ gas.

Ans. (a) reactive, (b) good, electricity, (c) more, (d) hydrogen

Q4. Mark ‘T’ if the statement is true and ‘F’ if it is false.

(a) Generally, non-metals react with acids.

(b) Sodium is a very reactive metal.

(c) Copper displaces zinc from sulphate solution.

(d) Coal can be drawn into wires.

Ans. (a)(F), (b)(T), (c)(F), (d)(F)

Q5. Some properties are listed in the following Table. Distinguish between metals and non-metals on the basis of these properties.

Q6. Give reasons for the following:

(a) Aluminium foils are used to wrap food items.

(b) Immersion rods for heating liquids are made up of metallic substances.

(c) Copper cannot displace zinc from its salt solution.

(d) Sodium and potassium are stored in kerosene.

Ans. (a) Aluminium is a metal so it is highly malleable (i.e. it can be beaten into thin sheets) and it does not react with food items and does not alter the taste. That’s why aluminium foils are used to wrap food items.

(b) Immersion rods need electric supply to get heated and in turn to heat liquids. And because metals are good conductors of heat and electricity, therefore immersion rods for heating liquids are made up of metallic substances.

(c) Copper is less reactive than zinc, so it cannot displace zinc from its salt solution.

(d) Sodium and potassium metals are very reactive. They react vigorously with oxygen and water. A lit of heat is generated in the reaction. Therefore, they are stored in kerosene.

Q7. Can you store lemon pickle in an aluminium utensil? Explain.

Ans. No, we cannot store lemon pickle in an aluminium utensil because aluminium is a metal and the pickle is acidic in nature. Metals react with acids to produce metal salts and hydrogen gas. So, the pickle can be spoil in the aluminium utensil.

Q8. In the following Table some substances given in Column A. In Column B some uses are given. Match the items in column A with those in Column B.

Q9. What happens when

(a) Dilute sulphuric acid is poured on a copper plate?

(b) Iron nails are placed in copper sulphate solution? Write word equations of the reactions involved.

Ans. (a) When sulphuric acid is poured on a copper plate, copper sulphate is made and hydrogen gas is evolved as per the following chemical equation:

Copper + Sulphuric acid —> Copper sulphate + Hydrogen gas

(b) Because iron is more reactive than copper, so when iron nails are poured in copper sulphate solution, it displaced the copper from copper sulphate solution and ferrous sulphate is made as per the following chemical equation:

Iron + Copper sulphate —> Ferrous sulphate + Copper

Q10. Saloni took a piece of burning charcoal and collected the gas evolved in a test tube.

(a) How will she find the nature of the gas?

(b) Write down word equations of all the reaction taking place in this process.

Ans. (a) Add some water in the test tube in which the gas is collected. Then cover the test tube and shake it well. Now teat the solution with both red and blue litmus. Blue litmus turns to red which shows that the gas is acidic in nature.

(b) Charcoal reacts with oxygen to form carbon dioxide gas.

Carbon (Charcoal) + Oxygen —> Carbon dioxide (gas)

Carbon dioxide gas reacts with water to from carbonic acid which is acidic in nature and turns blue litmus red.

Carbon dioxide + Water —> Carbonic acid

Q11. One day Reeta went to a jeweller’s shop with her mother. Her mother gave old gold jewellery to the goldsmith to polish. Next day when they brought the jeweller back, they found that there was a slight loss in its weight. Can you suggest a reason for loss in weight?

Ans. Gold jewellery are polished in a solution of aqua regia (mixture of nitric acid and hydrochloric acid). The outer layer of the gold dissolves in the acidic solution and the inner shiny layer is visible. Because of loss of upper layer of jewellery, its weight is reduced.

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Class 8th-Science: Chapter 5 – Coal and Petroleum

Natural Resources

Resources that are obtained from nature are known as natural resources.

For Example: Air, water, soil, minerals, sunlight, forests, moon etc.

In the light of the availability of various resources in nature, natural resources can be broadly classified into two kinds.

Types of Natural Resources

1.  Inexhaustible Natural Resources

These resources are present in unlinited quantity in nature and are not likely to be exhausted by human activities.

For Example: Sunlight, air, water, soil,

2.  Exhaustible Natural Resources

The amount of these resources in nature is limited. they can be exhausted by human activities.

For Example: forests, wildlife, minerals, coal, petroleum, natural gas etc.

Q.  Can we use all our natural resources forever?

Ans.  No, some natural resources (called exhaustible natural resources) are going to exhaust one day. So we cannot use them forever. For example: forests, wildlife, minerals, coal, petroleum, natural gas etc.

Q.  Can air, water and soil be exhausted by human activities?

Ans. No, these will not be exhausted by human activities.They are inexhaustible natural resources.

Q.  Is water a limitless resource?

Ans. Yes, water is a limitless resource because water cannot be finished or vanished from earth, it can be polluted by human activities but its end is not possible.


  1. Coal is as hard as stone and is black in colour.
  2. It is one of the fuels used to cook food.
  3. Earlier, it was used in railway engines to produce steam to run the engine.
  4. It is also used in thermal power plants to produce electricity.
  5. Coal is also used as a fuel in various industries.

Where do we get coal from and how is it formed?

About 300 million years ago the earth had dense forests in low lying wetland areas. Due to natural processes, like flooding, these forests got buried under soil. As more soil deposited over them, they were compressed. The temperature also rose as they sank deeper and deeper. Under high pressure and high temperature, dead plants got slowly converted to coal.

Q.  What is carbonisation?

Ans.  As coal contains mainly carbon, the slow process of conversion of dead vegetation into coal is called carbonisation.

A coal mine

When heated in air, coal burns and produces mainly carbon dioxide gas.

Carbon(coal) + Oxygen —> Carbon dioxide(gas) 

Coal is processed in industry to get some useful products such as coke, coal tar and coal gas.

A. Coke

  1. It is a tough, porous and black substance.
  2. It is almost pure form of carbon.
  3. Coke is used in the manufacture of steel and in the extraction of many metals.

B. Coal tar

  1. It is a black, thick liquid with unpleasant smell.
  2. It is a mixture of about 200 substances.
  3. Products obtained from coal tar are used as starting materials for manufacturing various substances used in everyday life and in industry, like synthetic dyes, drugs, explosives, perfumes, plastics, paints, photographic materials, roofing materials, etc.
  4. Interestingly, naphthalene balls used to repel moths and other insects are also obtained from coal tar.

These days, bitumen, a petroleum product, is used in place of coal-tar for metalling the roads.

C. Coal gas

Coal ia processed in industry to get some useful products such as coke, coal tar and coal gas.

  1. Coal gas is obtained during the processing of coal to get coke. 
  2. It is used as a fuel in many industries situated near the coal processing plants.

Coal gas was used for street lighting for the first time in London in 1810 and in New York around 1820. Now a days, it ia used as a source of heat rather than light.


1.  Petrol is used as a fule in light automobiles such as motor cycles/ scooters and cars.

2.  Heavy motor vehicles like trucks and tractors run on diesel.

3.  Petrol and diesel are obtained from a natural resource called petroleum.

Q.  Do you know how petroleum is formed?

Ans.  Petroleum was formed from organisms living in the sea. As these organisms died, their bodies settled at the bottom of the sea and got covered with layers of sand and clay. Over millions of years, absence of air, high temperature and high pressure transformed the dead organisms into petroleum and natural gas.

The world’s first oil well was drilled in pennsylvania, USA, in 1859. Eight years later, in 1867, oil was stuck at Makum in Assam. In India, oil is found in Assam, Gujarat, Mumbai High and in the river basins of Godavari and Krishna.

Refining of Petroleum

1.  Petroleum is a dark oily liquid.

2.  It has an unpleasant odour.

3.  It is a mixture of various contituents such as petroleum gas, petrol, diesel, lubricating oil, paraffin wax, etc.

Q.  What is refining?

Ans.  The process of separating the various constituents/ fractions of petroleum is known as refining. It is carried  out in a petroleum refinery.

Table 5.1 Various constituenta of petroleum and their uses

S.No Constituents of petroleum Uses

  1. Petroleum Gas in Liquid form (LPG) Fuel for home and industry
  2. Petrol Motor fuel, aviation fuel, solvent for dry cleaning
  3. Kerosene Fuel for stoves, lamps and for jet aircrafts
  4. Diesel Fuel for heavy motor vehicles, electric generators
  5. Lubricating oil Lubrication
  6. Paraffin wax Ointments, candles, vaseline etc.
  7. Bitumen Paints, road surfacing

Many useful substances are obtained from petroleum and natural gas. THese are termed as ‘Petrochemicals’.

These are used in the manufacture of detergents. fibres (polyester. nylon, acrylic ect.), polthene and other man-made plastics. Hydrogen gas obtained from natural gas, is used in the production of fertilisers (urea).

Due to its great commercial importance, petroleum is also called ‘black gold’. 

Fossils Fuel

Fossils:  The dead remains of living organisms are called fossils.

Fossil Fuels:  Fuels which are formed from the dead remains of organisms (called fossils) are called fossil fuels.

For Example:  Coal, petroleum and natural gas are fossil fuels.

Natural Gas

1.  Natural gas is a very important fossil fuel because it is easy to transport through pipes.

2.  Natural gas is stored under high pressure as compressed natural gas (CNG).

3.  CNG is used for power generation. It is now being used as a fuel for transport vehicles because it is less polluting. It is a cleaner fuel.

4.  The great advantage of CNG is that it can be used directly for burning in homes and factories where it can be supplied through pipes.

5.  Such a network of pipelines exists in vadodara (Gujarat), some parts of Delhi and other places.

6.  Natural gas is also used as a starting material for the manufacture of a number of chemicals and fertilisers.

7.  India has vast reserves of natural gas. In our country, natural gas has been found in Tripura, Rajasthan, Maharashtra and in the Krishna Godavari delta.

Q.  Can coal, petroleum and natural gas be prepared in the laboratory from dead organisms?

Ans.  No, Their formation is a very slow process and conditions for their formation cannot be created in the laboratory.

Tips to Save Petrol and Diesel

In India, the Petroleum Conservation Research Association (PCRA) advises people how to save petrol/diesel while driving. Their tips are:

Drive at a constant and moderate speed as far as possible,

Switch off the engine at traffic lights or at a place where you have to wait,

Ensure correct tyre pressure, and Ensure regular maintenance of the vehicle.

Chapter 5 Ncert Question Answer

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Class 8th-Science: Chapter 4- Materials Metals and Non-Metals

Definition of Metals & Non-Metals:


The materials which are hard, lustrous, malleable, ductile, sonorous and good conductors of heat and electricity are called metals.

For Example: iron, copper, aluminium, gold, silver, platinum, calcium, magnesium, etc.


The materials which are soft, dull in appearance, break down into powdery mass on tapping with hammer, not sonorous and poor conductors of heat and electricity are called non-metals.

For Example: sulphur, carbon, oxygen,

Examples of metals & Non-Metals

We see and use many materials in daily life which are made up of metals or non-metals.

MetalsIron, Aluminium, Gold, Silver, Copper, Platinum

Non-MetalsSulphur, Chlorine, Coal, Graphite

Q.  But how can we differentiate metals and non-metals?

Ans.  We can differentiate metals and non-metals on the basis of their physical and chemical properties.

Physical & Chemical Properties

Physical Properties:

 A physical property is a characteristic of a substance that can be observed or measured without changing its chemical identity or composition.

For Example: color, taste, mass, volume, density, temperature, melting point, boiling point, hardness, lustre, malleability, ductility, sonorous, conduction of heat, conduction of electricity.

Physical Properties of Metals:

1. Generally, metalsare hard

For Example: iron, copper, aluminium, silver, gold, etc. are hard.


Hardness of a substance refers to its resistance to bending, scratching, abrasion or cutting.

2. Metals are Lustrous.

For Example: Iron, copper, aluminium, silver, gold, etc. are lustrous.


Luster is the property of surface of a substance to reflect light due to which the substance appears shiny.

3. Generally, metals are Malleable.

For example: Silver Foil on Sweets, Aluminium Foil, Gold Foil (gold is the most malleable metals).


The property of metals by which they can be beaten into thin sheets is called malleability.

4. Metals are generally Ductie.

For Example: Copper wires, Silver wires Aluminium wires, Gold wires (gold is the most ductile metals).

5. Metals are Sonorous.


The things made of metals produce ringing sound when struck hard. this property of metal is called sonority and metals are called sonorous.

6. Metals are generally good conductors of heat

Q. Can you hold a hot metallic pan which is without a plastic or a wooden handle and not get hurt? Perhaps not! Why?

Ans. Yes, I will get hurt (with burn) if i hold a hot metallic pan which is without a plastic or a wooden handle.

Plastic and wood are non-conductor of heat. But the metallic pan is the conductor of heat. Without the handle, heat from hot pan will get conducted up to the handle, which in turn will become hot. And that can burn hand of pan holder.

7. Metals are good conductors of electricity

Q. How to check whether electricity can pass through an object or not?

Ans. By making an electric circuit, we can test whether electricity can pass through an object or not.

You can check electrical conductivity of various objects using this method like aluminium rod, gold ring, coal, sulphur etc.

Silver is the best conductor of electricity.

Physical Properties of Non-Metals:

1. Non-metals are generally soft. They are not hard.

For Example: Sulphur, coal, graphite etc. are soft.

2. Non-metals are mostly dull in appearance. They are non-lustrous.

For Example: Sulphur, coal etc. are dull in appearnce.

3. Non-metals are not malleable. They are brittle as they break down into powdery mass on tapping with hammer.

4. Non-metals are not ductile.

5. Non-metals are not sonorous.

6. Non-metals are generally poor conductors of heat.

7. Non-metals are generally poor conductors of electricity.

Chemical Properties:

A chemical property is a characteriatic or behavior of a substance that cn be observed when it undergoes a chemical change or reaction.

For Example: ability to rust, reactivity ect.

1. Reaction with Oxygen


Metal + Oxygen —> Metal Oxide

Magnesium + Oxygen —> Magnesium Oxide

2Mg + Oxygen —> 2MgO

Iron + Oxygen —> Iron Oxide

2Fe + O2 —> 2FeO

Copper + Oxygen —> Copper Oxide

2Cu + O2 —> 2CuO

Q. Recall the reaction by which rust is formed.

Ans. Rusting takes place on iron when iron comes in contact with oxygen in presence of water vapour in the atmosphere.

Iron + Oxygen + water —> Hydrated Iron(III) Oxide (Rust)

4Fe + 3O2 + H2O —> 2Fe2O3H2O (Rust)

Q. What do you observe? Is the solution acidic or basic?

Ans. The red litmus turns blue from red in this solution which confirms that the solution is basic in nature.

=> Oxide of iron is basic in nature.

Q. Now recall the activity of burning magnesium ribbon. The ash obtained on burning magnesium ribbon is dissolved in water and tested for its acidic / basic nature. Is the solution acidic or basic? How do you ascertain this?

Ans. Magnesium + Oxygen —> Magnesium Oxide ( 2Mg + O2 —> 2MgO )

The solution is basic. This is ascertained by pitting red litmus paper in the solution, which turns blue which is the test of basic nature of the solution.

=> Oxide of magnesium is also basic in nature.

In general, metallic oxides like Fe2O3, MgO, CuO etc. are basic in nature.

Q. Does copper also get rusted? I have seen a greenish deposit on the surface of copper vessels.

Ans. Yes copper also get rusted. When a copper vessel is exposed to moist air for long, it acquires a dull green coating. The green material is a mixture of copper hydroxide (Cu(OH)2) and copper carbonate (CuCO3). The following is the reaction 2Cu+H2O+CO2+O2 —> Cu (OH)2 + CuCO3


Non-metal + Oxygen —> Non-metal Oxide

Sulphur + Oxygen —> Sulphur Dioxide

S + O2 —> SO2

Carbon + Oxygen —> Carbon Dioxide

C + O2 —> CO2

Q(a). Specify what is formed as an end product

(i) when sulphur is heated in air?

(ii) when gas obtained from burning sulphur is dissolved in water?

Ans. (i) When sulphur is heated in air, sulphur dioxide is formed.

S + O2 —> OS2

(ii) When gas obtained from burning sulphur is dissolved in water, sulphurous acid is formed.

SO2 + H2O —> H2SO3

Q(b). What does litmus test reveals, when tested for this aqeous solution?

Ans. Blue litmus turns red in the aqeous solution, signifying acidic nature of sulphurous acid.

Q. Write the name of some laboratory acids and bases in Table 4.4. Identify the metal or non-metal present in them which forms oxides with oxygen.

Table 4.4 : Metals and Non-metals in Acids and Bases

2. Reaction with Water


Metal + Water —> Metal Oxide + Hydrogen Gas

Metal Oxide + Water —> Metal Hydroxide

Different metal reacts with water at rates. For example, sodium reacts vigorously with water, but other metals like iron reacts with water slowly.

Sodium metal is very reactive. It reacts vigorously with oxygen and water. A lot of heat is generated in the reaction. It is, therefore, stored in kerosene.

Q. When sodium is made to react with water, what happens to the beaker in which the reaction takes place. Also verify that the solution is acidic or basic?

Ans. The beaker becomes very hot because sodium reacts vigorously with water.

The solution thus obtained is basic in nature, as it turns red litmus blue.


Generally, non-metals do not react with water though they may be very reactive in air. Such non-metals are stored in water.

Q. Why is phosphorous stored in water?

Ans. Phosphorus is a very reactive non-metal. It catches fire if exposed to air. To prevent the contact of phosphorus with atmospheric oxygen, it is stored in water.

3. Reactions with Acids

Metal + Acid —> Metal Salt + Hydrogen Gas

Magnesium + Hydrochloric Acid —> Magnesium Chloride + Hydrogen Gas

Mg + HCl —> MgCl2 + H2

Metals react with acids and produce hydrogen gas that burns with a ‘pop’ sound but non-metals generally do not react with acids.

Q1. Is there a difference in the way metals and non-metals react with acids?

Ans. Yes, non-metals generally do not react with acids but metals react with acids and produce hydrogen gas that burns with a ‘pop’ sound.

Q2. What does the ‘pop’ sound indicate when a burning match stick is brought near the mouth of the test tube?

Ans. ‘Pop’ sound is produced when a burning matchstick is brought near the mouth of the test tube indicating the presence of hydrogen gas. It is the hydrogen gas that burns with a pop sound.

Q3. Name the metal which does not react with dilute hydrochloric acid even on heating but it reacts with sulphuric acid.

Ans. Copper does not react with dilute hydrochloric acid even on heating but it reacts with sulphuric acid.

4. Reactions with Bases

Some metals react with bases like (sodium hydroxide) and produce hydrogen gas that burns with a ‘pop’ sound. Reactions of non-metals with bases are complex.

5. Displacement Reactions

Displacement reaction is a chemical reaction in which a more reactive element displaces/ replaces/ removes a less reactive element from its compound.

For Example: Iron nails in copper sulphate solution.

Copper Sulphate + Iron —> Ferrous Sulphate + Copper

CuSO4 + Fe —> FeSO4 + Cu

Iron can displace copper from its compound

Q. Can copper displace iron from its compound? Can this reaction FeSO4 + Cu —> CuSO4 + Fe take place?

Ans. No, copper cannot displace iron from its compound because copper is less reactive than iron. Only more reactive metal can displace a less reactive metal from its compound. So the above reaction cannot take place.

Q. What is reactivity?

Ans. Reactivity is a measure of how readily a substance undergoes a chemical reaction. The reaction can involve the substance on its own or with other atoms or compounds, generally accompanied by a release of energy.

Q. What is the sequence of metals from more reactive to less reaction among zinc, iron and copper?

Ans. Zn > Fe > Cu

Q. What is the basic rule of displacement in a chemical reaction?

Ans. The rule is:

A more reactive metal can replace a less reactive metal, but a less reactive one cannot replace a more reactive metal.