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ScienceClass 8CBSE

Which of the following is not a combustible substance? (a) camphor (b) glass (c) straw alcohol

Soln: Answer is (b) glass Explanation: Camphor, glass, straw can burn in the air, and they are combustible substances. Glass will not burn in the air, and it is a non-combustible substance.

ScienceClass 8CBSE

Magnesium ribbon on burning in air produces: (a) magnesium oxide, water and light. (b) magnesium oxide and heat. (c) magnesium oxide, heat and light. magnesium oxide, water and heat.

oln: Answer is (c) magnesium oxide, heat and light Explanation: Magnesium reacts with atmospheric oxygen to get magnesium oxide by liberating heat and light.

ScienceClass 8CBSE

Which one of the following has the highest calorific value? (a) kerosene (b) biogas (c) LPG petrol

Soln: Answer is (c) LPG Explanation: Calorific represents the amount of heat generated when fuel burns completely. The calorific value of LPG is 55000-kilo joules/ Kg, which is high when compared to the calorific value of Kerosene, Biogas and petrol.

ScienceClass 8CBSE

A substance which reacts with oxygen giving heat, is called a combustible substance. Which one of the following is a combustible substance? (a) iron nail (b) glass (c) stone piece wood

Soln: Answer is (d) wood Explanation: Glass, iron nail and stone piece will not burn like wood hence they are not combustible. Wood burns in the air, and it is called a combustible substance.

ScienceClass 8CBSE

What steps would you suggest for the judicious use of fossil fuels?

Steps to take for the judicious use of fossil fuels Use fossil fuels only when it is Switch off automobile engine while standing in a Use solar energy wherever We can use natural gas in place of fossil fuels Use Alternate sources of energy like, solar, wind and biomass should be used in place of fossil

ScienceClass 8CBSE

Coal reserves are said to be enough to last for another hundred years. Do you think we need to worry in such case? Why or why not?

Coal reserves are said to be enough to last for another hundred years. Because there will be no availability of coal after the exhaust of existing coal resource. To produce coal it will take millions of years. Dead organisms should be buried in the earth and it should decompose in the absence oxygen. For all these process coal formation needs millions of years.

ScienceClass 8CBSE

Write some important uses of the various constituents of petroleum.

Soln: Constituents of Petroleum are petroleum gas, petrol, diesel, kerosene, lubricating oil, paraffin wax and Bitumen. Constituents of petroleum Uses Petroleum Gas (LPG) Fuel for home and industry Petrol Used as fuel for light automobiles. Kerosene Fuel for lamps, stoves and jet aircrafts Diesel Used as fuel for large automobiles and electric generators Lubricating oil Used as lubricant for engines Paraffin wax Used in preparation of Ointments, candles, vaseline etc. Bitumen Used in preparation of Paints, road surfacing

ScienceClass 8CBSE

Why petrol is exhaustible natural resource, whereas sunlight is not? Explain.

Petrol is a fossil fuel which is produced after years of decomposition of buried and plants deep down the earth. For producing petrol we need millions of years. If we use petrol higher than the requirement. Perol will get exhausted. Whereas sun is a continuous and unlimited source of energy. Sun is renewable resource of energy which will not get exhausted.

ScienceClass 8CBSE

Imagine that all the exhaustible natural resources are exhausted by human activities. Do you think survival of living beings would be possible.? If yes, why?, If not, why not?

If all the exhaustible natural resources are exhausted by human activities then survival of living beings would be impossible. Fossil fuels are very important source of energy for us today. On burning fossil fuel and give off heat and light. Heat produced can be used to cook food or to run engines such as automobile engines. It can be used to generate electricity as in powerhouse where the most common fuel used is coal.

ScienceClass 8CBSE

While driving what are the tips we must follow to save petrol/ diesel/natural gas?

Steps to follow while driving to save petrol/ diesel/natural gas 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 Ensure regular maintenance of the

ScienceClass 8CBSE

We read in newspapers that burning of fuels is a major cause of global warming. Explain why.

Burning of fuels lead to release of carbon-di-oxide, carbon-monoxide and SO2 gases. These are the green houses gases that not only increases the air pollution but also contribute for the global warming by trapping radiations from sun.

ScienceClass 8CBSE

We say fossil fuels will last only for a few hundred years. Comment.

Fossils fuels take millions of years to get converted into these fuels. Formation of fossil fuels requires specific conditions and it doesn’t happen quite often. Therefore, their limited stock will last only for a few hundred years.

ScienceClass 8CBSE

Name the products obtained and their uses when coal is processed in industry.

Coke, coal tar and coal gas are obtained when we process coal. Coke is used as reducing agent in the extraction of metals. Coal tar is used as starting material for manufacturing various sustances such as synthetic dyes, drugs, explosives, perfumes, paints etc. Coal gas is used as fuel.

ScienceClass 8CBSE

Match the items given in Column I with the items of Column II. Column I Column II (a) Used for road surfacing (i) Black gold (b) Natural gas (ii) Vaseline and candles (c) Petroleum (iii) Bitumen Paraffin wax (iv) CNG

Soln: Column I Column II Used for road surfacing (iii) Bitumen Natural gas (iv) CNG Petroleum (i) Black gold Paraffin wax (ii) Vaseline and candles

ScienceClass 8CBSE

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

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

ScienceClass 8CBSE

Write the characteristics and some important uses of coal.

Characteristics of coal. It is as hard as stone and is black in It is Combustible It is a fossil fuel When it is burned in air it releases CO Uses of Coal Coal is one of the fuels used to cook Earlier, it was used in railway engines to produce steam to run the It is also used in thermal power plants to produce Coal is also used as a fuel in various

ScienceClass 8CBSE

Write two important uses of coke.

Important uses of coke are as follows Coke is used as reducing agent in extraction of metal from its Coke is used in the manufacture of steel

ScienceClass 8CBSE

Sunlight and air are inexhaustible natural resources. Comment.

Soln: Sunlight is present in unlimited and they will not get exhausted by any means. Hence Sunlight is inexhaustible natural resources. Some natural resources are given in a Classify them into the exhaustible and inexhaustible natural resources. air, coal, natural gas, sunlight, petroleum, minerals, forests, oxygen. Soln: Exhaustible Inexhaustible coal air natural gas sunlight, petroleum, oxygen. minerals Forests

ScienceClass 8CBSE

Write True/False against the following statements. (a) Oxygen in air is an exhaustible natural resource. (b) Resources which are present in unlimited quantity in nature are called exhaustible natural resources. (c) Wildlife is an exhaustible natural resource. (d) Under high temperature and pressure, dead plants get slowly converted to coal. (e) CNG is less polluting fuel than petrol and diesel.

False Explanation: Oxygen is not an exhaustible natural resource. False, Explanation: Resources which are present in unlimited quantity in nature are called inexhaustible natural resources. True, True,

ScienceClass 8CBSE

Fill in the blanks. (a) The slow process of conversion of dead vegetation into coal is called . (b) Coal and petroleum are formed from the dead remains of organisms and are known as . (c) The black thick liquid with smell is known as coal tar. (d) During the processing of coal to get coke, coal tar and are also obtained. (e) The process of separating the various constituents of petroleum is known as . (f) Excessive burning of fossil fuels is a major cause of .

The slow process of conversion of dead vegetation into coal is called carbonisation. Coal and petroleum are formed from the dead remains of organisms and are known as fossil fuels. The black thick liquid with unpleasantsmell is known as coal During the processing of coal to get coke, coal tar and coal gasare also The process of separating the various constituents of petroleum is known as refining. Excessive burning of fossil fuels is a major cause of air pollution.

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