Which of the following states does NOT share its border with Nepal?

The correct answer is C, the theory of plate tectonics. Plate tectonics says the Earth's rigid outer shell is broken into plates that keep moving slowly, carried by convection currents in the mantle below. The theory took shape in the 1960s, after Harry Hess explained sea-floor spreading, and the term was given by Tuzo Wilson and others. There are seven major plates and many minor ones, moving a few centimetres a year, and almost all earthquakes, volcanoes, fold mountains and deep trenches occur where they meet. A is wrong because Alfred Wegener's continental drift of 1912 moved only the continents and could not name a force strong enough to do it. B is wrong because Pangaea is the name of the single super-continent, not a theory of motion. D is wrong because plate boundaries are the edges where plates meet, a part of the theory and not the theory itself. Exam tip: Wegener gave continental drift in 1912, Hess gave sea-floor spreading in 1960, and plate tectonics followed.

The correct answer is A, Aluminium manufacturing. Muri, a town in the Ranchi district of Jharkhand, has a large alumina refinery, so it is remembered as an aluminium centre. The works began in 1948 and are now run by Hindalco; they treat bauxite mined on the Lohardaga, Gumla and Palamu plateaus and turn it into alumina, the powder from which aluminium metal is smelted. Bauxite close by, coal-based power from the Damodar valley and a rail link are what put the industry there. B is wrong because copper in this region is smelted at Ghatsila in the Singhbhum copper belt. C is wrong because the steel plants of the area are at Jamshedpur and Bokaro, not Muri. D is wrong because the fertiliser unit of this belt stands at Sindri near Dhanbad. Exam tip: pair the Jharkhand towns - Muri with aluminium, Ghatsila with copper, Jamshedpur and Bokaro with steel, Sindri with fertiliser.

The correct answer is B, 1981. India's annual rate of population growth reached its peak in the two decades from 1961 to 1981 and has fallen in every census decade since 1981, which is why demographers date the turn to that year. The total number of people still rises, because a young age structure keeps the number of births high, but the rate at which it rises has come down; this stage, with death rates already low and birth rates now following them down, is the third stage of the demographic transition. The decade from 1911 to 1921 was the only one of the last century in which the population actually fell, mainly because of the influenza epidemic, so 1921 is called the demographic divide. A is wrong because the decline had begun a full decade before 1991. C is wrong because growth was still rising after 1951. D is wrong because the decade from 1971 to 1981 recorded the highest growth rate of all. Exam tip: 1921 is the demographic divide, growth peaks by 1981 and falls after it.

The correct answer is B, Young folded mountains. Young fold mountains were raised in the Tertiary period, only a few tens of millions of years ago in geological time, so erosion has had little time to wear them down and many of them are still rising as the plates behind them keep pushing. The Himalayas, the Alps, the Andes and the Rockies belong to this class, and the tallest summits on earth, Mount Everest and K2 among them, stand in the Himalaya and the Karakoram. A is wrong because old fold mountains such as the Aravallis, the Appalachians and the Urals were formed far earlier, and long erosion has reduced them to low rounded hills. C is wrong because residual mountains are only the harder remnants left behind after the surrounding rock was stripped away, so they stay low. D is wrong because block mountains, like the Vosges and the Black Forest, are raised by faulting between rift valleys and never reach such heights. Exam tip: the Himalaya is a young fold range and the highest, while the Aravalli is the oldest fold range in India.

The correct answer is C, Reduction in the vegetation cover to arrest landslide. Cutting the vegetation on a slope makes landslides more likely, not less, so it can never be a mitigation measure. Roots bind the soil and hold a slope together, and the leaf cover breaks the force of falling rain; where the forest is cleared, the loose soil slides down with the first heavy spell. The measures actually used are hazard zonation and mapping, retaining walls and benching of slopes, control of surface and subsurface drainage, afforestation on the slope, and limits on construction and blasting in fragile hill areas. A is wrong because a retaining wall holds the slipping mass in place and is a standard engineering step. B is wrong because hazard mapping marks the vulnerable belts so that building can be kept away from them. D is wrong because leading rainwater and spring flow away removes the water pressure that sets a slide off. Exam tip: afforestation helps and deforestation hurts; in India the Himalayas and the Western Ghats are the most landslide-prone regions.