Explanation:

- Delhi was declared the capital of India during the Delhi Durbar in December 1911.

- The British decided to shift the capital from Calcutta (now Kolkata) to Delhi for its historical significance and strategic location.

- Option 2: 1911 - This is the correct answer. Delhi became the capital of India this year.

- Option 1: 1901 - This is incorrect. At that time, Calcutta was still the capital.

- Option 3: 1913 - Incorrect as well. By 1913, Delhi was already serving as the capital.

- Option 4: 1921 - Also incorrect. Delhi had already been the capital for about a decade by then.

- This decision was a turning point, making Delhi the political center of India.