Khadins are used in Rajasthan to :

Which of the following combination of terms has no fossil fuel ?

The use of one of the following is eco-friendly. This one is :

In a village, farmers started cultivating crops all around a lake which was always filled with water. They added lot of materials W to the soil in their fields to increase the yield of crops. Soon they found that the whole surface of water in the lake was covered with a green layer made up of tiny organisms X. After some time, the fish present in the lake started dying in large numbers because they could not get sufficient Y due to a process Z which had occurred in lake water and drained out all the Y present in the water of lake.

(a) What do you think materials W are ?

(b) Name (i) X, and (ii) Y.

(c) What is the process Z known as?

(d) What happens during the process Z which uses up all the Y present in lake water?

(e) What does this example tell us about the use of materials like W?

There were lot of organisms A in the crop fields in an area. These organisms used to feed on organisms B also present in the crop fields but which damaged the standing crops. One day some people arrived in the fields and killed all the organisms A so that they could remove their C for making fancy items which were in great demand. Due to large scale killing of A, the population of B increased too much damaging all the crops in the area and causing a famine-like situation. Apart from A, there is another organism D which can also kill and eat B. Name A, B, C and D.