Correct Answer: At its Lahore Session in 1929

Solution : The correct option is At its Lahore Session in 1929.

The All India Congress formally adopted the demand for 'Purna Swaraj' or full independence for India, on December 19, 1929. This historic decision was made during the Lahore session of the Indian National Congress. During this session, the Indian National Congress declared January 26, 1930, as Independence Day and hoisted the tri-colour flag, marking the beginning of the Civil Disobedience Movement against British colonial rule.