The Constitution of India came into force fully, and India became a republic, on:

The Constitution of India came into force fully on 26 January 1950, and India became a sovereign democratic republic on that day.

Why 26 January was chosen:

• On 26 January 1930, the Indian National Congress had observed "Purna Swaraj Day" (Independence Day) for the first time, following the Lahore session resolution of 1929.
• From 1930 to 1947, 26 January was celebrated as Independence Day by the nationalists.
• To honour this tradition, the Constitution was brought into force on 26 January.

What happened on that day:

India ceased to be a British dominion, and became a republic.

Dr. Rajendra Prasad was sworn in as the first President of India.

The Governor-General's post came to an end; C. Rajagopalachari had been the last Governor-General.

The Constituent Assembly became the Provisional Parliament of India.

The Federal Court became the Supreme Court of India.

The State Emblem was adopted.

The Indian Independence Act (1947) and the Government of India Act (1935) were repealed (except the Abolition of Privy Council Jurisdiction Act, 1949).

Republic Day:

• 26 January is celebrated every year as Republic Day, a national holiday.
• The main celebrations are held in New Delhi, with a grand parade on the Kartavya Path, which displays India's military strength and cultural diversity.
• The President of India takes the salute, and a foreign head of state or government is usually invited as the chief guest.
• The celebrations end with the "Beating Retreat" ceremony on 29 January, at Vijay Chowk.

The three national days:

Independence Day (15 August), Republic Day (26 January) and Gandhi Jayanti (2 October) are the three national holidays of India.

Why not the other options?

• ✗15 August 1947 was the date of Independence; 26 November 1949 was the date of the adoption of the Constitution; 24 January 1950 was the date of the signing.