Army Day is celebrated in India on 15 January because on this day in 1949

The correct answer is B, the Constitution of India came into force. The Constitution took effect on 26 January 1950 and India became a sovereign republic. The date was chosen on purpose, because the Indian National Congress had declared Purna Swaraj, or complete independence, on 26 January 1930, and the founders wished to honour that pledge.

Option A is wrong because independence came on 15 August 1947, which is observed as Independence Day. Option C is wrong because the Constituent Assembly adopted the Constitution on 26 November 1949, and that day is kept as Constitution Day, earlier called Law Day; the two-month gap between adoption and commencement is exactly what this question tests. Option D is wrong because the first general election was held in 1951 and 1952, after the Republic had come into being.

The correct answer is B, Swami Vivekananda. He was born on 12 January 1863, and the Government of India declared his birthday National Youth Day so that his call to the young would be placed before students each year. It has been observed since 1985.

Option A, Bhagat Singh, was born in September and is remembered on 23 March, the day he was hanged in 1931 along with Sukhdev and Rajguru, which is kept as Shaheed Diwas. Option C, Subhas Chandra Bose, was born on 23 January 1897, and that date is observed as Parakram Diwas. Option D, Jawaharlal Nehru, was born on 14 November 1889, which is kept as Children's Day. All four dates fall in the list of national days, so the question is really about matching the man to his own date.

The correct answer is B, the discovery of the Raman effect. Sir C. V. Raman announced his discovery of the scattering of light, now called the Raman effect, on 28 February 1928, and it won him the Nobel Prize in Physics in 1930, the first for an Indian in the sciences. The day has been observed since 1987.

Option A is wrong because the Indian Science Congress held its first session in January 1914 and is not the reason for this day. Option C is wrong because Aryabhata, India's first satellite, was launched on 19 April 1975, a date kept by the space community and not as National Science Day. Option D is wrong because the Pokhran tests of 11 May 1998 are marked as National Technology Day, which is the commonest confusion in this question. Keep the pair apart: 28 February is science, 11 May is technology.

The correct answer is A, Dr S. Radhakrishnan. He was born on 5 September 1888, was a philosopher and teacher before entering public life, and served as the first Vice-President and the second President of India. When admirers wished to celebrate his birthday, he asked that it be kept as Teachers' Day instead.

Option B, Maulana Abul Kalam Azad, was independent India's first Education Minister, and his birthday, 11 November, is observed as National Education Day, which makes him the strongest distractor. Option C, Dr Zakir Husain, was an educationist and the third President of India, but no national day is named for him. Option D, Dr Rajendra Prasad, was the first President of India and presided over the Constituent Assembly. Remember the pair: 5 September for teachers and 11 November for education.

The correct answer is B, Sir M. Visvesvaraya. Mokshagundam Visvesvaraya was born on 15 September 1861, served as the Diwan of Mysore, and built the Krishnarajasagara dam and the system of automatic sluice gates that made his name. He was awarded the Bharat Ratna in 1955, and Engineers' Day honours him.

Option A, Homi Jehangir Bhabha, was the architect of India's atomic energy programme and is remembered as a physicist rather than an engineer. Option C, Vikram Sarabhai, founded India's space programme, and Indian space landmarks are tied to him instead. Option D, A. P. J. Abdul Kalam, was an aerospace scientist and the eleventh President of India; his birthday, 15 October, is observed as World Students' Day. A candidate who notices the day names the engineer, not the scientist, gets this right at once.