CDS 2020 Previous Year GK Questions with Answers

The correct answer is C, Cu + PbCl2 → CuCl2 + Pb. Copper is less reactive than lead, so it cannot push lead out of its compound.

In a displacement reaction, a more reactive metal takes the place of a less reactive metal in its salt solution. The reactivity series, from more to less reactive, runs: potassium, sodium, calcium, magnesium, aluminium, zinc, iron, lead, hydrogen, copper, mercury, silver, gold. Magnesium, zinc and iron are all above copper, so each of them displaces copper from copper sulphate; the blue solution fades and reddish-brown copper is deposited. Copper, however, lies below lead, so it has no power to displace lead from lead chloride.

A is wrong: iron is more reactive than copper, so this reaction takes place, the classic iron nail in copper sulphate experiment.

B is wrong: zinc is above copper in the series and readily displaces it.

D is wrong: magnesium is far more reactive than copper and displaces it easily.

Exam tip: a metal displaces only those below it in the reactivity series: K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Hg, Ag, Au.

The correct answer is A, The fission bomb dropped at Hiroshima. Little Boy was the code name of the uranium fission bomb dropped by the United States on the Japanese city of Hiroshima on 6 August 1945, the first use of a nuclear weapon in war. Three days later, on 9 August, a plutonium bomb named Fat Man was dropped on Nagasaki, and Japan surrendered shortly afterwards. B is wrong because the bomb dropped at Nagasaki was Fat Man, and it was a fission bomb as well, not a fusion or hydrogen bomb, which came only in the 1950s. C is wrong because the first nuclear device tested by the United States was code-named Trinity and was exploded in New Mexico in July 1945. D is wrong because North Korea's first nuclear test came decades later and has no connection with these code names.

The correct answer is B, The National Commission for Scheduled Tribes. Article 338A was inserted by the 89th Constitutional Amendment Act, 2003, which split the earlier joint commission into two separate bodies and gave the Scheduled Tribes a commission of their own from 2004. It has a chairperson, a vice-chairperson and three other members appointed by the President, and it investigates complaints about tribal safeguards, advises on planning for tribal development and reports to the President, who places the report before Parliament. Option A is wrong because the National Commission for Scheduled Castes rests on Article 338, the article as it stood before the split. Option C is wrong because the National Commission for Backward Classes became a constitutional body only in 2018, under Article 338B, through the 102nd Amendment. Option D is wrong because the National Commission for Women is a statutory body set up by an Act of Parliament in 1990 and has no article of its own. Exam tip: 338 for SCs, 338A for STs, 338B for OBCs.

The correct answer is D, Uruguay. The Tropic of Capricorn runs at about 23.5 degrees south and misses Uruguay, which lies further south between roughly 30 and 35 degrees. In South America the line crosses Chile, Argentina, Paraguay and Brazil; going east it passes through Namibia, Botswana, South Africa, Mozambique, Madagascar and Australia, in all ten countries. It marks the farthest point south at which the Sun is overhead, which happens on 22 December, the summer solstice of the southern hemisphere. Option A is wrong because the line crosses northern Chile near the Atacama desert. Option B is wrong because it passes through Brazil just north of Sao Paulo, and the city sits almost on it. Option C is wrong because it runs across Paraguay, cutting the country into a northern tropical part and a southern temperate part. Exam tip: the Tropic of Cancer crosses eight states of India, while the Tropic of Capricorn passes through no part of India at all.

The correct answer is B, Separate electorates for untouchables. The conference met in Bombay in 1931 and resolved that the depressed classes must be allowed to elect their own representatives through separate electorates, a demand Dr B. R. Ambedkar carried to the Second Round Table Conference in London the same year. The British accepted it in the Communal Award of 1932, which gave separate electorates to the depressed classes. Gandhi opposed this as a step that would split Hindu society and began a fast unto death in Yerwada jail. The deadlock ended with the Poona Pact of September 1932, under which separate electorates were given up and replaced by a larger number of seats reserved for the depressed classes inside the general electorate. Option A is wrong because universal adult suffrage was a later, wider demand of the national movement. Option C is wrong because the conference spoke for the depressed classes, not minorities in general. Option D is wrong because the form of the state was not its subject. Exam tip: Communal Award 1932, then Poona Pact 1932 - separate electorates traded for reserved seats.

The correct answer is C. Ultraviolet light is a transverse wave, not a longitudinal one, so this statement is the wrong one. In an electromagnetic wave the electric and magnetic fields vibrate at right angles to each other and to the direction the wave travels, which is the definition of a transverse wave. Longitudinal waves need a material to squeeze and stretch, and sound is the standard example. Option A is correct because ultraviolet light sits in the electromagnetic spectrum between visible light and X-rays. Option B is correct because electromagnetic waves need no medium and cross empty space, which is how the Sun's ultraviolet rays reach the earth. Option D is correct because ultraviolet wavelengths run from about 400 nanometres down to 10 nanometres, shorter than violet light, and this higher energy is what burns skin and is absorbed by the ozone layer. Exam tip: all electromagnetic waves are transverse; only mechanical waves such as sound can be longitudinal.

The correct answer is C, the Supreme Court and High Courts only, because the Constitution gives writ jurisdiction to these two courts alone. The Supreme Court issues writs under Article 32, which is itself a fundamental right and can be used only to enforce fundamental rights. A High Court issues them under Article 226, and its power is wider: it covers fundamental rights and any other legal right as well. The five writs are habeas corpus, mandamus, prohibition, certiorari and quo warranto. Option A is wrong because the High Courts have this power too, and under a broader article. Option B is wrong because Article 32 lets a person go straight to the Supreme Court. Option D is wrong because district and subordinate courts have no writ jurisdiction at all; they can grant other remedies, but not writs. Exam tip: Article 32 for the Supreme Court and Article 226 for High Courts, with Article 226 the wider of the two.

The correct answer is D, Kyushu Island of Japan. Kyushu is one of the four main islands of the Japanese archipelago and is of volcanic origin, built by the eruptions of an island arc where one plate dives beneath another; Mount Aso on it has one of the largest volcanic calderas in the world. It is not a coral reef island at all. Option A is wrong as a choice because the Great Barrier Reef off the Queensland coast is the classic coral structure, the largest in the world. Option B is wrong because the Rainbow Reef of Fiji, in the Somosomo Strait, is a well known coral reef in the tropical Pacific. Option C is wrong because Swaraj Island, formerly called Havelock Island, lies in the Andaman group, where the islands are ringed by fringing coral reefs. The lesson to carry away is that tropical islands are built in two very different ways, by volcanic activity and by the slow growth of coral, and the question tests whether you can tell them apart.

The correct answer is A, the north eastern coast of Australia. The Great Barrier Reef stretches for well over two thousand kilometres along the Queensland coast in the Coral Sea, off the north eastern shore of Australia, and is the largest structure on earth built by living organisms. It lies there because the conditions a reef needs are all present together: shallow water on a wide continental shelf, sea temperature that stays warm through the year, clear water that lets sunlight reach the algae living inside the coral polyps, and normal salinity undisturbed by a great river. Option B is wrong because the western coast faces the cool waters of the Indian Ocean and carries only small fringing reefs. Option C is wrong because the northern coast is muddied by river discharge into the Arafura Sea. Option D is wrong because the southern coast lies in cooler temperate latitudes where reef building corals cannot grow. Remember also that reefs are called the rainforests of the sea.

The correct answer is C, Lahore. The Lahore session of the Indian National Congress, presided over by Jawaharlal Nehru, adopted the Purna Swaraj or complete independence resolution. At midnight on 31 December 1929, Nehru hoisted the tricolour on the banks of the river Ravi. The Congress then fixed 26 January 1930 as Purna Swaraj Day for the whole country, and the session also authorised the Working Committee to launch civil disobedience, which began with the Dandi March in March 1930. That is why the Constitution was brought into force on 26 January 1950. A is wrong, because the Ahmedabad session of 1921 met during the Non-Cooperation Movement, with Hakim Ajmal Khan as acting president. B is wrong, because the Calcutta session of 1928 under Motilal Nehru only gave the British one year to accept dominion status. D is wrong, because the Lucknow session of 1916 is known for the Congress-League pact and the reunion of moderates and extremists. Exam tip: Lahore 1929, Nehru, Purna Swaraj; 26 January 1930, the first Independence Day.

The correct answer is B, The National Commission for Scheduled Tribes. Article 338A sets up this Commission as a constitutional body. It was inserted by the 89th Amendment Act, 2003, which split the old combined National Commission for Scheduled Castes and Scheduled Tribes into two; the separate ST Commission began work in 2004. It has a Chairperson, a Vice-Chairperson and three members appointed by the President by warrant under his hand and seal, and it reports to the President, who has the report laid before Parliament. An easy hook: the letter A was added when the tribes got a Commission of their own. A is wrong, because the National Commission for Scheduled Castes comes under Article 338. C is wrong, because the National Commission for Backward Classes got constitutional status under Article 338B through the 102nd Amendment, 2018. D is wrong, because the National Commission for Women is a statutory body set up under the National Commission for Women Act, 1990. Exam tip: 338 SC, 338A ST, 338B backward classes; the Women's Commission is only statutory.