What is the number of the Sustainable Development Goals (SDGs) set by UN 2030 Agenda for sustainable Development?

The correct answer is A, Nicobar pigeon. An endemic species is one that occurs naturally in one particular area and nowhere else, and the Nicobar pigeon is the textbook Indian example, living in the forests of the Nicobar group of islands; the Andaman wild pig and the Narcondam hornbill are usually listed beside it. Island populations turn endemic easily, because the sea keeps them cut off and they evolve on their own, and that isolation also makes them fragile, since clearing the forest or bringing in a new predator can wipe out the whole species at one stroke. B is wrong because the Indian wild ass, though now confined to the Rann of Kutch, is a subspecies of the Asiatic wild ass found across Asia. C is wrong because the desert fox ranges over the deserts of Asia and Africa. D is wrong because the Indian one-horned rhino lives in Nepal as well as in Assam and West Bengal. Exam tip: endemic means found in one area only, and the Nicobar pigeon and the Narcondam hornbill are the stock examples.

The correct answer is D, SDG 15. Goal 15, called Life on Land, is the goal for land ecosystems, and its wording covers forests, desertification, land degradation and the loss of biodiversity. The 17 Sustainable Development Goals were adopted by the United Nations in 2015 as the heart of the 2030 Agenda, and they are to be reached by 2030. Goal 15 takes in forest cover, protected areas, the Red List of threatened species and the fight against poaching and the trafficking of wildlife, while Goal 14, Life Below Water, does the same work for the seas. A is wrong because SDG 12 is about responsible consumption and production. B is wrong because SDG 7 is about affordable and clean energy. C is wrong because SDG 17 is about partnerships for the goals. Exam tip: hold the pair together - SDG 14 is Life Below Water for the oceans and SDG 15 is Life on Land for forests and soil.

The correct answer is C, Carbon monoxide. Carbon monoxide is a dangerous air pollutant, but it is not counted among the major greenhouse gases, because it absorbs very little of the infrared heat leaving the earth. A greenhouse gas is one that traps this outgoing heat and warms the lower atmosphere. The major ones are carbon dioxide, methane, nitrous oxide, water vapour and the fluorinated gases such as HFCs, PFCs and sulphur hexafluoride. A is wrong because carbon dioxide, released by burning coal, oil and gas, adds the largest share to global warming. B is wrong because methane, which comes from paddy fields, cattle and landfills, traps far more heat per molecule than carbon dioxide does. D is wrong because nitrous oxide, mostly from nitrogen fertilisers, is a strong and long-lived greenhouse gas. Exam tip: carbon monoxide and sulphur dioxide are pollutants, not greenhouse gases; the gases listed in the Kyoto Protocol are carbon dioxide, methane, nitrous oxide and the F-gases.

The correct answer is D, Overgrazing. Overgrazing is a cause of soil degradation, not a way to conserve soil, so it is the option that does not belong. When too many animals feed on the same patch, the grass cover is eaten down to the roots and hooves loosen the bare topsoil, which wind and running water then carry away; in dry regions this is a main road to desertification. A is wrong as an answer because crop rotation is a genuine conservation method, since changing the crop each season restores nitrogen and other nutrients instead of draining one of them. B is wrong as an answer because terrace farming cuts a slope into steps, slowing runoff so that water soaks in rather than washing the soil down. C is wrong as an answer because tree roots bind the soil and shelter belts of trees break the force of the wind. Exam tip: contour ploughing, terracing, strip cropping and shelter belts conserve soil; overgrazing and deforestation destroy it.

The correct answer is D, Nitrogen. Nitrogen makes up about 78 per cent of the atmosphere, yet it is not a greenhouse gas. A molecule traps heat only if it can absorb outgoing infrared radiation, and that needs vibrations which change the spread of electric charge in the molecule. Nitrogen is a simple molecule of two identical atoms, so it is transparent to infrared; the same is true of oxygen. The gases that do trap heat are water vapour, carbon dioxide, methane, nitrous oxide, ozone and the halocarbons, and together they keep the earth about 33 degrees Celsius warmer than it would otherwise be. Option A is wrong because water vapour is the most abundant greenhouse gas of all. Option B is wrong because chlorofluorocarbons are powerful greenhouse gases that also destroy the ozone layer, which is why the Montreal Protocol phases them out. Option C is wrong because methane traps far more heat per molecule than carbon dioxide. Exam tip: nitrogen and oxygen are not greenhouse gases, though they make up most of the air.