Oxygen is harmful for (a) ferns (b) nitrogen fixing bacteria (c) chara (d) mango tree

The two forms of oxygen found in the atmosphere are (a) water and ozone (b) water and oxygen (c) ozone and oxygen (d) water and carbon dioxide

Top-soil contains the following (а) Humus and living organisms only (b) Humus and soil particles only (c) Humus, living organisms and plants (d) Humus, living organisms and soil particles.

The atmosphere of the Earth is heated by radiations which are mainly (a) radiated by the Sun (b) re-radiated by land (c) re-radiated by water (d) re-radiated by land and water

Soil erosion can be prevented by (a) raising forests (b) deforestation (c) excessive use of fertiliser (d) overgrazing by animals

Oxygen is returned to the atmosphere mainly by (a) burning of fossil fuel (b) respiration (c) photosynthesis (d) fungi

Which of the following is not a greenhouse gas? (a) Methane (b) Carbon dioxide (c) Carbon monoxide (d) Ammonia

One of the following processes is not a step involved in the water-cycle operating in nature (a) evaporation (b) transpiration (c) precipitation (d) photosynthesis

‘Ozone-hole’ means (a) a large sized hole in the ozone layer (b) thinning of the ozone layer (c) small holes scattered in the ozone layer (d) thickening of ozone in the ozone layer

Total Earth’s surface covered by water is (a) 75% (b) 60% (c) 85% (d) 50%

Growth of lichens on barren rocks is followed by the growth of (a) moss (b) ferns (c) gymnosperms (d) algae

Biotic component of the biosphere is not constituted by (a) producers (b) consumers (c) decomposer (d) air