Explanation:

• The Simon Commission came to India in 1927 to generate a report on how well the 1919 Government of India Act was working. 
• The Salt March, which took place from 12 March to 6 April 1930 in India, was an act of civil disobedience led by Mohandas Gandhi to protest British rule in India.
• The 'Gandhi-Irwin Pact' was a political agreement signed by Mohandas Karamchand Gandhi and Lord Irwin, the then Viceroy of India, on 5 March 1931 before the second Round Table Conference in London.
• The Poona Pact is an agreement between M K Gandhi and B R Ambedkar signed in the Yerwada Central Jail, Poona on September 24th, 1932 on behalf of the depressed class.

Hence option 4th is correct.