The pyramid of energy in any ecosystem is

The correct answer is D, Ecotone. An ecotone is the transition zone where two different ecosystems meet and mix, such as the belt between a grassland and a forest, an estuary between a river and the sea, or a mangrove strip between land and ocean. It holds species of both neighbouring communities along with a few of its own, so the number of species and their density are often higher in it. This crowding at the edge is called the edge effect, and species found only in such a belt are called edge species. A is wrong because the ecosphere means the whole living world of the earth taken together with its environment. B is wrong because ecoboundary is not a term used in ecology. C is wrong because ecotwin is not an ecological term either. Exam tip: tie ecotone to the edge effect, and keep ecotone, a zone, apart from ecocline, a gradual gradient.

The correct answer is D, 17. The 2030 Agenda for Sustainable Development sets 17 Sustainable Development Goals, and these are broken into 169 targets. The United Nations General Assembly adopted the agenda in September 2015 and the goals came into force on 1 January 2016, taking over from the eight Millennium Development Goals that ran from 2000 to 2015. Goal 1 is no poverty, Goal 2 is zero hunger, Goal 13 is climate action and Goal 17 is partnerships for the goals. In India, NITI Aayog tracks them and publishes the SDG India Index. A, B and C are wrong because 19, 15 and 12 are not the count of the goals; 15 and 12 are themselves goal numbers, life on land and responsible consumption, which is the trap in this question. Exam tip: fix the three numbers together - 17 goals, 169 targets, adopted September 2015 for the period up to 2030.

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.