The Gobind Sagar reservoir was created by which dam?

The correct answer is A, hilly terrains. Hydel or hydroelectric power depends on head, the vertical distance through which water falls on to the turbine, and on a narrow valley in hard rock where a tall dam can hold a deep reservoir. Hills supply both, which is why the great hydro stations of the country stand in the Himalaya and the Western Ghats, at Tehri, Nathpa Jhakri, Koyna and Idukki. Option B, desert areas, is wrong because a desert has neither perennial flow nor the gradient needed, and high evaporation would empty a reservoir. Option C, plains, is wrong because the gradient there is too gentle to give useful head; plains carry barrages for irrigation and navigation, such as Farakka, rather than high dams. Option D, oceans, is wrong because a dam needs a river channel to close; the sea is used for tidal and wave power, which is a different technology altogether.

The correct answer is B, Bhagirathi. The Tehri Dam stands on the Bhagirathi in the Tehri Garhwal district of Uttarakhand, close to the confluence of the Bhagirathi and the Bhilangana, and it is an earth and rock fill dam, the tallest in India at about two hundred and sixty metres. Option A, the Alaknanda, is the other headstream of the Ganga and meets the Bhagirathi at Devprayag to form the Ganga; it carries the Vishnuprayag and Srinagar projects but not Tehri, and it is the strongest distractor because the two streams are always learnt together. Option C, the Sutlej, carries the Bhakra Dam in Himachal Pradesh and the Nathpa Jhakri power project, and Bhakra is the dam most often confused with Tehri in height questions. Option D, the Yamuna, carries barrages at Tajewala and Hathnikund and the Lakhwar project, and is not the river of the Tehri Dam.

The correct answer is B, Mahanadi. The Hirakud Dam lies across the Mahanadi above Sambalpur in Odisha, and counting the main dam together with its earthen dykes it is among the longest dams in the world; it was built chiefly to control the floods that used to devastate coastal Odisha, and it also serves irrigation and power. Option A, the Godavari, is the second longest river of India and carries the Sriram Sagar project and the Polavaram project, not Hirakud. Option C, the Brahmani, also flows through Odisha and carries the Rengali dam, which makes it the sharpest distractor here because the state is the same. Option D, the Subarnarekha, flows through Jharkhand, West Bengal and Odisha and carries the Chandil and Icha projects. Remember the pair Hirakud with Mahanadi as one unit, and the fact that it is a flood control dam first.

The correct answer is C, Tarapur. The Tarapur Atomic Power Station in the Palghar district of Maharashtra was commissioned in 1969 and was the first nuclear power station in India and in Asia to generate electricity commercially; its first two units were boiling water reactors built with American assistance. Option A, Kalpakkam, is the Madras Atomic Power Station in Tamil Nadu, the first station of wholly indigenous design, and it also holds the Indira Gandhi Centre for Atomic Research and the fast breeder reactor programme. Option B, Rawatbhata, is the Rajasthan Atomic Power Station, where the first pressurised heavy water reactor was built in collaboration with Canada, and it is the commonest wrong choice because it too claims a first. Option D, Kudankulam in Tamil Nadu, is the most recent of the four and uses Russian pressurised water reactors of the VVER type.

The correct answer is B, Jammu and Kashmir. The Chenab Rail Bridge was built on the Udhampur Srinagar Baramulla rail link in the Reasi district of Jammu and Kashmir, and its steel arch carries the track about three hundred and fifty nine metres above the bed of the Chenab, which makes it the highest railway arch bridge in the world. Option A, Himachal Pradesh, has the Kalka Shimla and Kangra valley narrow gauge lines with many masonry viaducts, but none of that height. Option C, Uttarakhand, carries the rail head at Rishikesh and the Rishikesh Karnaprayag line under construction, and its bridges do not reach this height. Option D, Ladakh, has no railway line at all, which alone rules it out; it is placed among the options because candidates associate the Himalaya with Ladakh. The Chenab rises in Himachal Pradesh, so read whether the question asks where the river rises or where the bridge stands.