National Science Day is observed in India on 28 February to commemorate

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 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.

The correct answer is B, Major Dhyan Chand. The hockey player was born on 29 August 1905 and won Olympic gold with India in 1928, 1932 and 1936. National Sports Day is observed on his birthday, and the national sports awards are usually presented on that date.

Option A, Milkha Singh, was the athlete known as the Flying Sikh, who finished fourth in the 400 metres at the 1960 Rome Olympics, but no national day carries his name. Option C, Sachin Tendulkar, is a cricketer and a Bharat Ratna, and although his birthday is widely noted, it is not a national day. Option D, K. D. Jadhav, won India's first individual Olympic medal, a wrestling bronze in 1952, a fact worth knowing separately. The sports day belongs to hockey and to Dhyan Chand.