Five definitions: hydrosphere, nuclear energy, smog, abiotic component, fossil fuels

Five of the seven terms are defined, as the question allows: (i), (ii), (iii), (iv) and (v).

(i) The hydrosphere

The hydrosphere is all the water of the Earth: the seas and oceans, rivers, lakes and wetlands, groundwater, and the ice and water vapour that form part of the water cycle. Water evaporates from the seas and fresh waters, forms clouds in the atmosphere and falls as rain on the land, so the hydrosphere is linked to the atmosphere and lithosphere through the hydrological cycle. It gives drinking water, irrigation and fish; the Ganga basin is one Indian example of its importance.

(ii) Nuclear energy

Nuclear energy is the energy held in the nucleus of an atom. In a nuclear reactor it is released by fission, the splitting of the nucleus of a heavy atom such as uranium, and the heat produced is used to make electricity. It produces little air pollution, but its radioactive wastes and the risk of accidents can cause serious environmental damage; India's reactors at Tarapur and Kudankulam are examples of its use.

(iii) Smog

Smog (smoke + fog) is a thick, polluted haze formed when smoke and gases such as sulphur oxides mix with fog in still, cold air that is trapped near the ground and cannot rise. It cuts visibility and causes coughing, sore throat and lung disorders; the London smog, which turned the city's fog black into a pea-soup smog, is the classic case. Winter smog over Delhi and the Indo-Gangetic plain is a present-day Indian example.

(iv) An abiotic component

An abiotic component is a non-living part of an ecosystem: inorganic materials such as air, water and soil, together with physical factors such as light and temperature. It forms the ecosystem's structure along with the biotic components (producers, consumers and decomposers), and the two interact constantly. Sunlight and water in a pond are abiotic components.

(v) Fossil fuels

Fossil fuels are the hydrocarbon fuels coal, oil and natural gas, formed from the plant life of ancient prehistoric forests that was buried and fossilised. They are non-renewable, because the stock cannot be replaced once it is used, and drilling, processing, transporting and using them pollutes air and water. Coal burnt in India's thermal power stations is a familiar example.