We can use organic wastes to produce energy by a very cheap method. The procedure is as follows:
(i) There are many types of organic waste such as dead plants, animals and kitchen wastes. This waste is put into a drum called biogas digester where it is decomposed by the bacteria.
(ii) After decomposition, this mixture starts producing methane and carbon dioxide gas. This gas is collected in the cylinder.
(iii) A tube is connected with this cylinder through which the gas is obtained and used for cooking and lighting purpose.

(a) Copper and Iron are the minerals that are used by us every day.
(b) Two regions that are rich in natural gas resources are Jaisalmer and Krishna-Godavari delta. 

Solar Energy: The energy obtained from the sun is called the solar energy.
Importance:
(i) Solar energy is free of cost and does not cause any pollution.
(ii) It is a non-conventional source of energy.
(iii) It will reduce the dependence of rural households on firewood and dung cakes.

Non-Conventional Resources : The resources which are not so common in use, but can be used as alternate resources and are renewable are known as Non-Conventional Resources. For example, Solar Energy, Wind Energy, Geothermal Energy.
There is a pressing need to use these sources of energy for the following reasons :
(i) The growing consumption of energy has resulted in the country becoming increasingly dependent on fossil fuels such as coal, oil and gas.
(ii) Rising prices of oil and gas and their potential shortages have raised uncertainties about the security of energy supply in future, which, in turn, has serious repercussions on the growth of the national economy.
(iii) Moreover, increasing use of fossil fuels also causes serious environmental problems.

Some advantages of biogas are:
(i) It is very cheap to produce.
(ii) Biogas can be easily generated.
(iii) It can be produced by making use of bio-wastes.
(iv) It is largely used in rural areas.

The advantages of coal are:
(i) It is abundantly available in the earth.
(ii) It is one of the most primitive source of energy. 
The disadvantages of coal are:
(i) The transportation cost of coal is very high.
(ii) It is one of the most polluting fuel as it produces lots of smoke when burnt and is responsible for global warming.

Power resources can be classified as :
1. Conventional Resources: Include power resources that are common in use for long time. For example, Firewood, Hydel Power, Coal. 
2. Non-Conventional Resources : Include those resources that are not so common in use, but can be used as alternate resources. For example, Solar Energy, Wind Energy, Geothermal Energy.

Un the basis of metals, minerals are classified into two categories;
(i) Metallic minerals
(ii) Non-Metallic minerals
(i) Metallic Minerals : Metallic minerals are those which are good conductors of heat and electricity
because of the presence of the metals inside. These metallic minerals are further classified on the
basis of iron content as:
(a) Ferrous minerals: The minerals which have iron content are called ferrous minerals, e.g.
Manganese.
(b) Non-ferrous minerals: The minerals which do not contain iron in them but, they certainly have
some other metal in them, e.g. Copper. 
(ii) Non-Metallic minerals: These minerals are not molded into any form and are a bad conductor of electricity. Limestone is a good example of nonmetallic minerals.

Generally, it is believed that mining is the only form of mineral extraction. hilt ~here are many other techniques for mineral extraction.
These are :
(i)Mining: Mining is the process of excavation of the minerals both from deep as well as shallow areas. There are two methods of mining:
(a) Open cast mining : It is a mining technique in which material is extracted by digging a large hole, rather than tunneling.
(b) Shaft mining : It is a type of underground mining done by use of a rnineshaft. It may also refer to the act of excavation the shaft itself.
(ii) Drilling: It is a type of shaft mining. It is generally used for oil and natural gas excavation.
(iii) Quarrying: It is generally used to extract minerals which lie near the surface by simply digging.