The Partition of Bengal made by Lord Curzon in 1905 lasted until:

Option B is correct. At the Delhi Durbar on 12 December 1911, King George V announced the annulment of the 1905 partition and the reunification of Bengal. The change took effect from 1 October 1912, and the capital moved from Calcutta to Delhi in the same announcement. Bihar and Orissa were separated as a new province.

• A: The WWI explanation is a popular myth. The partition was reversed in 1911, before the war began in 1914. The real pressure came from the Swadeshi and anti-partition agitation.
• C: Gandhi launched Civil Disobedience in 1930, nearly two decades after the partition was undone. The dates alone eliminate it.
• D: The 1947 Partition is a different event. East Bengal becoming East Pakistan was a consequence of 1947, not the end of the 1905 partition.

Core concept: the Partition of Bengal and the Swadeshi movement. For Mains, it shows how mass boycott and agitation can force a colonial government to reverse a decision.

Trap: Candidates pick A because of the war-loyalty story, or D because the later division of Bengal is more familiar. Fix the 1911 Durbar date firmly.