According to the Census of 2011, which of the following states has the highest density of population per km²?

The correct answer is C, 1000. Salinity is the quantity of dissolved salt, in grams, present in one thousand grams of sea water, so it is read as parts per thousand. The average salinity of the oceans is about thirty five parts per thousand, which means about thirty five grams of salt in a kilogram of sea water. Sodium chloride makes up the largest share of it, followed by magnesium chloride, magnesium sulphate and calcium sulphate. Salinity rises where evaporation is high and the inflow of fresh water is low, which is why the Red Sea reaches about forty one parts per thousand, and it falls near the mouths of large rivers and in polar waters fed by melting ice. A, B and D are wrong because a base of ten thousand, a hundred or ten grams would not give the parts per thousand figure that oceanographers actually use. Exam tip: salinity is grams of salt per 1000 grams of sea water, and the ocean average is about 35 parts per thousand.

The correct answer is D, Tundra. In Koppen’s classification the group of cold climates, marked E, holds two types, the tundra climate and the ice cap climate. The tundra belt lies mainly north of the Arctic Circle along the northern edges of North America, Europe and Asia. Its summers are short and cool, the average temperature of the warmest month stays below ten degrees Celsius, the subsoil stays frozen as permafrost, and the plant cover is limited to mosses, lichens and low shrubs, with no trees. A is wrong because the humid subtropical type belongs to the warm temperate group, which covers northern India, southern China and the south eastern United States. C is wrong because the humid continental type falls in the cold snow forest group, one step milder than the polar group. B is wrong because highland climate is kept as a separate group, where conditions change with altitude rather than with latitude. Exam tip: Koppen’s groups are A tropical, B dry, C warm temperate, D cold snow forest, E cold or polar and H highland.

The correct answer is A, Vijayawada. Vijayawada in Andhra Pradesh has a large coal based thermal power station on the Krishna river, named after Dr Narla Tata Rao, but no nuclear plant. India’s nuclear stations are run by the Nuclear Power Corporation of India Limited, and the other three names in the question are all on that list. B is wrong because Narora, in Bulandshahr district of Uttar Pradesh on the bank of the Ganga, has a station with two pressurised heavy water reactors. C is wrong because Tarapur in Palghar district of Maharashtra is the country’s oldest nuclear station, commissioned in 1969 with boiling water reactors built with American help. D is wrong because Rawatbhata in Rajasthan stands on the Chambal near the Rana Pratap Sagar dam and carries the largest number of units of any Indian nuclear station. Kakrapar in Gujarat, Kaiga in Karnataka, and Kalpakkam and Kudankulam in Tamil Nadu complete the set. Exam tip: Tarapur was India’s first nuclear power station; Vijayawada is thermal, not nuclear.

The correct answer is B, West Bengal. India's first jute mill was set up at Rishra, on the bank of the Hooghly near Serampore in Bengal, in 1855 by George Auckland. The industry stayed along that river because the Hooghly belt had everything it needed together: jute grown in the deltaic plains of Bengal, cheap water transport, coal from the Raniganj field, labour from Bihar and Odisha, and the port of Kolkata to ship sacking and hessian out. Partition in 1947 left most of the jute fields in East Pakistan while the mills stayed in India, which hurt the industry badly. West Bengal still has the largest number of jute mills and the highest output. A is wrong because Odisha has only a few mills. C is wrong because Assam grows jute but its mills came later. D is wrong because Bihar's mills, at Katihar and elsewhere, also came after Bengal's. Exam tip: first jute mill at Rishra on the Hooghly in 1855; West Bengal leads in jute.

The correct answer is A, Odisha. Odisha is the largest producer of bauxite in India and accounts for more than half of the country's output. Its ore lies in the plateau belt of Koraput and Kalahandi, where the Panchpatmali deposit worked by NALCO is the biggest in the country, and it is also mined in Sundargarh and Bolangir. Bauxite is the ore from which alumina and then aluminium is obtained, so the state carries large refineries and smelters as well. Gujarat, Jharkhand, Chhattisgarh, Maharashtra and Madhya Pradesh follow at a distance. B is wrong because Bihar has almost no bauxite; its old reserves went to Jharkhand when the state was divided in 2000. C is wrong because Madhya Pradesh mines bauxite in Katni and Balaghat but on a far smaller scale. D is wrong because Jharkhand's mines in Lohardaga and Gumla also yield much less than Odisha's. Exam tip: Odisha leads in bauxite, chromite and iron ore; Panchpatmali in Koraput is the largest bauxite deposit.