Class 8 Science Chapter 3 Question Answers - Coal and Petroleum

Q26: How burning of fossil fuels causes air pollution?

Ans: Pollutants that come from the combustion of fossil fuels include sulphur dioxide (SO2),nitrogen oxides (NOx), ground-level ozone, particulate matter (PM), carbon monoxide(CO), carbon dioxide (CO2), volatile organic compounds (VOC) including benzene, some heavy metals and a number of other pollutants which contribute to smog, acid rain, climate change, and health, environmental and economic concerns.

Q27: What are natural resources? Explain with examples.
Ans. The resources provided by nature or obtained from the nature are called natural resources. For example: air, water, soil and sunlight etc.

Q28: Classify the natural resources on the basis of their availability.
 Ans. On the basis of the availability various, natural resources in nature can be classified in the following two groups:
(i) Inexhaustible natural resources: Air, Water, Soil, Sunlight, etc.
(ii) Exhaustible natural resources: Forests, Wildlife, Minerals and Coal etc.
Q29: What are fossil fuels? Name the main fossil fuels.    
 Ans. The remains of dead plants and animals are called fossils. The fuels formed by the remains of dead plants and animals are called fossil fuels. Main fossil fuels are: coal petroleum and natural gas. 
Q30: What is coke? Write its uses.
 Ans. Coke is a tough porous and black substance. It is almost the purest form of carbon. It is formed by heating coal in the absence of air.

Uses: 
(i) It is used in manufacture of steel.
(ii) It is used in the extraction of metals. 
Q31: What is coal tar? What are its uses?
Ans. Coal tar is a black thick liquid. It is a mixture of about 200 substances.

Uses: 
(i) It is used as a source of various useful substances.
(ii) It is used to get naphthaline which is used to repel moths and other insects.
(iii) It is used to make road surface.
Q32: What is coal gas? Write the uses of coal gas.
Ans. Coal gas is a by-product formed when coal is heated in absence of air.

Uses: 
(i) It is used as fuel in many industries.
(ii) Previously it was used for street lighting in London in 1810.

Q.33: What is petroleum? Why is it called black gold?    
Ans. Petroleum is a dark oily liquid. It is a mixture of various constituents. Its constituents are very useful. Due to its great commercial importance petroleum is also called black gold.
Q34: Where and when was the first oil well drilled? (i) in world and (ii) in India.
 Ans. (i) The world’s first oil well was drilled in Pennsylvania, (U.S.A.), in 1859.
(ii) In India, the first oil well was drilled at Makum (Assam) in 1867.

Q35: Why is natural gas called a very important fossil fuel in these days?    
 Ans. Natural gas is a very important fossil fuel because it is easy to transport through pipes. It is used in the form of CNG as fuel and generation of power.
 Q36: Why is CNG called a clean fuel?
 Ans. CNG is called a clean fuel because:
(i) It does not produce any pollution.
(ii) No residue is left after burning of CNG.
(iii) It burns completely in the air.
Q37: What are the harmful effects of using fossil fuels?
 Ans. Harmful effects of burning fossil fuels are as following:
(i) Burning of fossil fuels cause air pollution.
(ii) They also cause global warming because they produce greenhouse gas like carbon dioxide on burning.
Q38: Make a list of various materials used by us in daily life and classify them as natural and man-made materials (Refer to Activity 5.1).

Ans.