NCERT Solutions for Class 8 Science Chapter 5 - Coal And Petroleum

Share with your friends Share Share Share twitter

Answer:

Plastic is a manmade material and therefore, not a natural resource.

Hence, the correct answer is option D. 
 

Answer:

Sunlight is an inexhaustible natural resource.

Hence, the correct answer is option C.

Answer:

Exhaustible natural resources are resources which are limited in nature and can be exhausted by human activities. Examples include forests, wildlife, minerals, coal, petroleum, natural gas etc.

Hence, the correct answer is option D.

Answer:

Compressed Natural Gas (CNG) is another fossil fuel and much cleaner fuel than coal. It is not obtained from coal.

Hence, the correct answer is option D.

Answer:

Exhaustible natural resources are limited in quantity. They can be exhausted by human activities. 

Hence, the correct answer is option C.

Answer:

Fossil fuels are obtained from dead remains of living organisms (fossils).

Hence, the correct answer is option D.

Answer:

Coal is formed from the remains of vegetation only under high pressure and high temperature over millions of years.

Hence, the correct answer is option A.

Answer:

The slow process of conversion of dead vegetation into coal is called carbonisation.

Hence, the correct answer is option A.

Answer:

Naphthalene balls are obtained from coal tar and are used as moth repellant.

Hence, the correct answer is option C.

Answer:

Petroleum is a mixture of various constituents such as petroleum gas, petrol, diesel, lubricating oil, paraffin wax, etc. Coke is produced from coal.

Hence, the correct answer is option D.

Answer:

Petroleum was formed from organisms living in the sea. Over millions of years, absence of air, high temperature and high pressure transformed the dead organisms into petroleum and natural gas.

Hence, the correct answer is option C.

Answer:

Natural gas is a naturally occurring hydrocarbon gas mixture of combustible gases. It is formed underground by the decomposition of organic materials in plants and animals. The transport of natural gas is difficult through pipelines because the friction in the pipeline causes the gas to heat up.

Hence, the correct answer is option A.

Answer:

Petroleum is lighter than water and present as a separate layer above water as they do not mix with each other. They can be separated by the process of decantation. 

Answer:

The full form of CNG is Compressed Natural Gas. It is considered to be a better fuel than petrol because it is less polluting and a cleaner fuel.

Answer:

Kerosene is the petroleum product used as fuel for stoves, lamps and jet aircrafts.

Answer:

(a) Coal is one of the fuels used to cook food.
(b) When heated in air, coal burns and produces mainly carbon dioxide gas.
(c) Coal tar is a black, thick liquid with an unpleasant smell.
(d) Petroleum, coal and natural gas are fossil fuels.
(e) Forests and coal are exhaustible natural resources.

Answer:

(a) Coal is obtained from mines.
(b) Petroleum is a fossil fuel.
(c) Refinery is a place where various fractions of petroleum are separated.
(d) Kerosene is a fuel used in jet crafts.
(e) Sunlight is an example of inexhaustible natural resources.

Answer:

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

Answer:

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

Answer:

Sunlight and air are present in unlimited quantity in nature and are not likely to be exhausted by human activities. Therefore, they are known as inexhaustible natural resources.

Answer:

Exhaustible natural resources: Coal, natural gas, petroleum, minerals, and forests
Inexhaustible natural resources: Air, sunlight, and oxygen

Answer:

Two important uses of coke are:

• It is used in the manufacture of steel.
• It is used in the extraction of many metals. 

Answer:

Characteristics of coal:

• It is as hard as stone and is black in colour.
• When heated in air, coal burns and produces mainly carbon dioxide gas.

• Coal is one of the fuels used to cook food.
• It is used in thermal power plants to produce electricity.
• It is used as a fuel in various industries.

Answer:

Oil layer is present above water layer because oil is lighter than water and do not mix with it.

Answer:

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 temperature and high pressure, dead plants got slowly converted into coal.

Answer:

Answer:

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

Uses:

• Coke: It is used in the manufacture of steel and in the extraction of many metals.
• Coal tar: Products obtained from coal tar are used as starting materials for manufacturing synthetic dyes, explosives, perfumes, plastics, photographic materials, roofing materials, etc.
• Coal gas: It is used as a fuel in many industries situated near the coal processing plants.

Answer:

Fossil fuels are exhaustible natural resources because their amount is limited in nature. They were formed from the dead remains of living organisms (fossils) over millions of years. Under high temperature and high pressure, dead plants got slowly converted to coal. Also, petroleum and natural gas were formed from organisms living in the sea over millions of years in the absence of air, high pressure and high temperature. They are the main fuels used in transport vehicles and industries. Hence, the fossil fuels are being used across the world widely and will last only for a few hundred years.

Answer:

Burning of fossil fuels leads to production of carbon dioxide and other harmful gases which cause air pollution and greenhouse effect. Nowadays, a lot of such gases are being released into the atmosphere because of large number of vehicles and industries. Petrol is used as a fuel in motor cycles, scooters and cars. Heavy motor vehicles like trucks and tractors run on diesel. It is also used in thermal power plants to produce electricity. Coal gas is used as a fuel in many industries situated near the coal processing plants. This has led to the accumulation of carbon dioxide in the atmosphere. As a result, the average temperature of the earth’s atmosphere is gradually increasing which is called global warming. 

Answer:

The tips that must be followed to save petrol/diesel/natural gas while driving are:

• Ensure correct tyre pressure.
• Ensure regular maintenance of the vehicle.
• Drive at a constant and moderate speed so that wastage of fuels can be conserved
• Switch off the engine at traffic lights or at a place where you have to wait.
• Avoid using the air-conditioner whenever possible. 

Answer:

Yes, survival of living beings would be possible. In fact, the air quality will become very good.
Humans could then completely switch over to inexhaustible natural resources such as sunlight and air. Instead of fossil fuels, the use of alternative fuels would become a trend for our energy requirements. These could be solar energy, hydropower and wind energy.

Answer:

The amount of petrol in nature is limited. It is obtained from petroleum which was formed from transformation of dead organisms living in the sea over millions of years in absence of air under high temperature and high pressure. And, it is being widely used used to run motor cycles and cars. So, it will be exhausted by human activities in near future. Hence, it is exhaustible natural resource. On the other hand, sunlight is present in unlimited quantity in nature and are not likely to be exhausted by human activities. Therefore it is not an exhaustible natural resource.

Answer:

Some important uses of the various constituents of petroleum are as follows:

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

Answer:

Yes, we need to worry because coal is an exhaustible natural resource. It was formed from the dead vegetation under high pressure and high temperature over millions of years. Therefore, it is also called a fossil fuel. It would take million of years to form coal after the present coal reserves would be depleted. A lot of industries are dependent on coal such as steel manufacturing industries and industries involved in extraction of metals. Thermal power plants use coal to produce electricity. Hence, we need to use coal judiciously so that it is available for a longer period of time. Also, we should switch to cleaner fuels for our energy requirements.

Answer:

The following steps should be adopted for the judicious use of fossil fuels:

• Carpooling should be encouraged.
• More use of public transport.
• Use of bicycles instead of motor cycles and scooters while going for shopping in nearby areas.
• Engines of motor vehicles should be switched off at red light areas and places where one has to wait.
• Vehicles should be regularly checked for maintenance.

Answer: