The 1929 Session of Indian National Congress is of significance in the history of the Freedom Movement because the

The answer is B. At the Lahore session of December 1929, presided over by Jawaharlal Nehru, the Congress adopted Purna Swaraj (complete independence) as its goal. The resolution also asked people to observe 26 January 1930 as Independence Day, and that date became the base for the Civil Disobedience Movement launched in 1930.

• A is wrong: Self-government within the Empire, or Dominion Status, was the demand of the Calcutta session of 1928, after the Nehru Report. Lahore moved beyond it.
• C is wrong: The Non-Cooperation Movement was launched in 1920 after the Calcutta special session and the Nagpur session. Civil Disobedience came in 1930, after Lahore.
• D is wrong: The Congress boycotted the First Round Table Conference (1930-31). It participated only after the Gandhi-Irwin Pact of 1931.

The core concept is the shift from constitutional demands to a demand for full sovereignty, which opened the way for mass civil disobedience. For Mains, this is a good link to the evolution of the national movement's goals and its strategies.

Trap: Candidates often confuse the 1928 Dominion Status demand with the 1929 Purna Swaraj resolution and pick A.