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ScienceClass 8CBSE

Which of the following represents the correct match for items in Column A with those in Column B. Column A Column B I. Nylon (i) Thermoplastic II. PVC (ii) Thermosetting plastic III. Bakelite (iii) Fibre (a) I-(ii), II-(iii), III-(i) (b) I-(iii), II-(i), III-(ii) (c) I-(ii), II-(i), III-(iii) (d) I-(iii), II-(ii), III-(i)

Answer is (c) I-(ii), II-(i), III-(iii)

ScienceClass 8CBSE

The most suitable material for the preparation of handles of cooking utensils is (a) Polythene (b) PVC (c) Nylon Bakelite

Soln: Answer is (d) Bakelite Explanation: Bakelite is a bad conductor of heat and it does not get soft on heating hence Bakelite is used to prepare handles of cooking utensils.

ScienceClass 8CBSE

Which of the following is not a common property of plastics? (a) Non-reactive (b) Light in weight (c) Durable Good conductor of electricity

Soln: Answer is (d) Good conductor of electricity Explanation: Plastic is a bad conductor of electricity.

ScienceClass 8CBSE

The material similar to silk in appearance is (a) Nylon (b) Rayon (c) Polyester Terylene

Soln: Answer is (b) Rayon Explanation: Rayon is obtained by chemical treatment of wood pulp. Rayon is cheaper than silk and can be woven like silk.

ScienceClass 8CBSE

Polycot is obtained by mixing (a) nylon and wool (b) polyester and wool (c) nylon and cotton polyester and cotton

Soln: Answer is (d) polyester and cotton

ScienceClass 8CBSE

Which is a thermosetting plastic? (a) Melamine (b) Polythene (c) PVC Nylon

Soln: Answer is (a) Melamine Explanation: Thermosetting plastics when moulded once can not be softened by heating. Examples are bakelite and melamine.

ScienceClass 8CBSE

Which of the following is a source of rayon? (a) Wool (b) PET (c) Wood pulp Silk

Soln: Answer is (a) Wool Explanation: Rayon is obtained by chemical treatment of wool pulp.

ScienceClass 8CBSE

Pick the synthetic fibre out of the following? (a) Cotton (b) Nylon (c) Jute Wool

Soln: Answer is (b) Nylon Explanation: Cotton and Jute are from plant sources, Wool is of animal source whereas Nylon is a synthetic fibre.

ScienceClass 8CBSE

Why should we save paper?

We should save paper for the flowing reason Trees are cut to manufacture In order to save the trees paper should be saved. Saving paper can help in saving water used to manufacture the Usage of chemical can be reduced which will reduce the water

ScienceClass 8CBSE

How does deforestation lead to frequent floods and droughts?

Deforestation will reduce the water holding capacity of the soil due to lack of trees. This reduces infiltration of water into the ground which increase the chances of flood. Cutting of trees leads to accumulation of Carbon-di- oxide in the atmosphere. CO2 traps heat rays from sun which are reflected by earth. This results in increase of temperature on earth. Increase in temperature disturbs water cycle which causes draughts and floods.

ScienceClass 8CBSE

Is deforestation associated with global warming? Explain.

Plants absorbs Carbon-di-oxide from atmosphere and releases oxygen. Cutting of trees leads to accumulation of Carbon-di-oxide in the atmosphere. CO2 traps heat rays from sun which are reflected by earth. This results in increase of temperature on earth.

ScienceClass 8CBSE

What is the unique feature of the biodiversity found in Panchmarhi Biosphere Reserve?

The biodiversity found in Panchmarhi Biosphere Reserve is similar to that found in upper Himalayan peaks and lower Western Ghats.

ScienceClass 8CBSE

Mention the aim of Forest (Conservation) Act.

Aim of Forest (Conservation) Act are as follows To conserve natural forests and the animals present in the To meet the basic needs of the people living in the

ScienceClass 8CBSE

Does soil erosion affect the fertility of soil? How?

Soil erosion leads to wash out of soil fertile layer of soil. This leads to desertification of land due to lack of fertle soil.

ScienceClass 8CBSE

A new species X is introduced in a forest. How is it likely to affect the local species of that area?

Introduction of new species in a forest lead to competition for food and place. Hence it will affect the native species present in the forest

ScienceClass 8CBSE

How are even small animals important in an ecosystem?

Every organism forms a part of food chain and ecosystem. Hence every organism is important to balance ecosystem.

ScienceClass 8CBSE

Why are endemic organisms in greater danger of becoming extinct?

Endemic organisms are those which can live in particular geographical location. Any disturbance to their natural habitat will affect the endemic animals adversely hence they are in great danger of becoming extinct.

ScienceClass 8CBSE

Why are wildlife sanctuaries important for conservation of plants and animals?

Wildlife sanctuaries important for conservation of plants and animals because in these areas poaching or killing animals, and disturbing animals by any means of human activity are prohibited. More over in wild life sanctuaries animals can live in their natural environment. This promotes their breeding and population increase.

ScienceClass 8CBSE

Can a forest regenerate naturally in a short period of time?

It takes long period of time to regenerate the forest naturally.

ScienceClass 8CBSE

In our country, large patches of forests are being cleared for cultivation of crops. The environmental impact of such a practice will lead to (a) soil erosion (b) soil conservation (c) soil pollution soil fertility

Answer is (a) soil erosion Explanation: Due to cutting of trees, there will no roots to hold the soil, because of this top soil erodes by the action of wind.

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