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NCERT 8th Class (CBSE) Science: Coal and Petroleum

Question: Classify various materials we use in our lives.

Answer: All the materials we use can be broadly classified into two groups:

  1. Natural Resources: Natural resources are those resources which are present in our nature, gifted by God. They can be freely used. Soil, air, sunlight, water, etc., are some natural resources.
  2. Man-made Resources: Man-made resources are those resources which are formed by various efforts of man and are artificial. Plastics, fibres, electricity, etc., are all artificial resources.

On availability of materials natural materials can further be classified as:

  1. Inexhaustible Natural Resources: Those resources which are present in unlimited quantity and will never get exhausted by human activities. Sunlight, air, soil, etc., are some inexhaustible natural resources.
  2. Exhaustible Natural Resources: Those resources which are available in limited amount and will get finished by human activities. Petroleum, coal, wildlife, forests, etc. are some examples of exhaustible natural resources.

Question: Differentiate between renewable and non-renewable resources, giving two examples of each.

Answer: Differentiation is as follows:

Renewable resource
Non-renewable resources
1. Resources which are replace naturally within a reasonable period of time through natural processes are known as renewable resources.
1. Resources which once used up cannot be replaced naturally within a reasonable period of time are known as Non-renewable resources.
2. Examples: sunlight, oxygen, groundwater.
2. Examples: fuels like petroleum, natural gas, coal, top soil, etc.

Question: What are fossil fuels?

Answer: Fuel derived from dead remains of plants and animals are called fossil fuels e.g. coal, petroleum and natural gas.

Question: Why should fossil fuels not be wasted?

Answer: Fossil fuels are non renewable sources of energy, which if exhausted cannot be regenerated. This is because they take millions of years to form. So, these should not be wasted. Moreover, they should be used with care and control so that their existing stock could last as long as possible.

Question: How is coke obtained?

Answer: The residue left behind when destructive distillation of coal is carried out is coke. It is almost pure form of carbon.

Question: What are the advantages of using natural gas as a fuel?

Answer: The advantages of using natural gas as a fuel are:

  1. It can be easily transported through pipes.
  2. It is a clean non-polluting fuel for vehicles.
  3. It is economical and easy to handle.

Question: Why is there a rapid increase in our energy consumption?

Answer: There is a rapid increase in our energy consumption due to two main reasons. They are:

  1. The increase in population.
  2. Industrialization and development of new technologies.

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