Which one of the following is not a main greenhouse gas?

The correct answer is B, Producers. Producers, the green plants and algae, are the most numerous living part of an ecosystem because every other organism depends on them for food. They make their own food by photosynthesis using sunlight, so they form the first trophic level of every food chain. Only about 10 per cent of the energy passes from one level to the next (Lindeman's ten per cent law), so each higher level can support fewer organisms. This gives the upright pyramid of numbers in a grassland: many grass plants, fewer grasshoppers, fewer frogs, and very few snakes and hawks. A is wrong because primary consumers, the herbivores, feed on producers and are fewer than them. C is wrong because secondary consumers, the small carnivores, are fewer still. D is wrong because tertiary consumers, the top carnivores such as the tiger or eagle, are the fewest of all. Exam tip: Producer → primary consumer → secondary consumer → tertiary consumer; about 90 per cent of energy is lost at each step; in a single-tree ecosystem the pyramid of numbers is inverted.

The correct answer is D, Blue Flag. In 2018 the Union Environment Ministry started a pilot project to clean up and develop selected beaches so that they could win the Blue Flag. The Blue Flag is an international eco-label given by the Foundation for Environmental Education (FEE), based in Copenhagen, Denmark; it began in France in 1985. A beach must meet strict standards on water quality, environmental education, safety and services, and environmental management. India's programme for this is called BEAMS (Beach Environment and Aesthetics Management Services), and in 2020 Shivrajpur in Gujarat was among the first Indian beaches to receive the Blue Flag. A is wrong because Swachh Bharat is the national sanitation mission started in 2014, not a beach label. B is wrong because the Green Flag is a different award, used in the UK for well-kept parks and green spaces. C is wrong because Clean India is only the English name of the Swachh Bharat campaign. Exam tip: Blue Flag = beach eco-label by FEE, Denmark; India's scheme = BEAMS; the first eight Indian Blue Flag beaches were certified in 2020.

The correct answer is A, Madhya Pradesh. Kanha Tiger Reserve lies in the Mandla and Balaghat districts of Madhya Pradesh, in the Maikal hills at the eastern end of the Satpura range. It was among the first nine tiger reserves created when Project Tiger was launched in 1973. Kanha is best known for saving the hard-ground barasingha, a swamp deer that had almost died out and is now the state animal of Madhya Pradesh. Its open sal forests and grassy meadows make it one of the best places in India to see tigers in the wild. Madhya Pradesh's other well-known tiger reserves include Bandhavgarh, Panna, Pench and Satpura. B is wrong because Karnataka's famous tiger reserves are Bandipur and Nagarhole. C is wrong because Odisha's main tiger reserve is Similipal. D is wrong because Maharashtra's best-known tiger reserves are Tadoba-Andhari and Melghat. Exam tip: Kanha = Madhya Pradesh = barasingha; one of the first nine Project Tiger reserves of 1973.

The correct answer is C, Polythene bag. Polythene is a synthetic plastic that bacteria and fungi cannot break down, so it is non-biodegradable. A plastic bag can stay in soil or water for hundreds of years. Biodegradable waste is anything that decomposers can break down into simple, harmless substances, and it usually comes from plants or animals. Plastic bags choke drains and cause waterlogging, are swallowed by cattle and sea animals, and give off toxic gases when burnt, which is why their use must be reduced and the bags reused and recycled rather than thrown away. Waste is best kept in two bins: wet (biodegradable) and dry (non-biodegradable). A is wrong because vegetable peels rot within days and make good compost. B is wrong because dead leaves decay into humus that enriches the soil. D is wrong because a rotting fruit is already being broken down by microbes. Exam tip: if microbes can eat it, it is biodegradable; plastic, glass, metal cans and DDT are not.

The correct answer is B, acid rain. Rain with a pH below 5.6 is called acid rain. Even clean rain is slightly acidic, with a pH of about 5.6, because carbon dioxide from the air dissolves in it to form weak carbonic acid; that is why 5.6, not 7, is the dividing line. Rain turns more acidic when sulphur dioxide and nitrogen oxides from coal-fired power plants, factories and vehicles mix with water vapour and form sulphuric and nitric acids. Acid rain corrodes marble and metal, kills fish in lakes and harms soil and forests. In India the best-known example is the damage to the Taj Mahal's white marble, often called 'marble cancer'. A is wrong because alkaline rain would have a pH above 7. C is wrong because 'mineral rain' is not a scientific term. D is wrong because hard water means water with dissolved calcium and magnesium salts; it is not a measure of how acidic rain is. Exam tip: rain pH below 5.6 = acid rain; culprits SO₂ and NOₓ; victim marble, as in the Taj Mahal.