Option 1: Simon Commission - The Simon Commission was appointed in 1927 by the British Government to recommend constitutional reforms in India. It was met with strong opposition as it consisted of all British members and no Indian members. The Congress and other nationalist groups boycotted the Commission`s arrival in India. Therefore, the Simon Commission happened after the Gaya Session of Congress.

Option 2: Gaya Session of Congress - The Gaya Session of Congress took place in 1922. It was an important session where the Non-Cooperation Movement, initiated by Mahatma Gandhi, was officially launched. This session marked a significant shift in the freedom struggle as it advocated for nonviolent resistance against British rule. The decision to start the Non-Cooperation Movement at this session makes it the earliest event among the given options.

Option 3: Tripuri Session of Congress - The Tripuri Session of Congress occurred in 1939. It was an important session where Subhas Chandra Bose was elected as the President of the Congress. This session was marked by the formation of the Forward Bloc, a group within the Congress advocating for a more radical approach towards independence. Therefore, the Tripuri Session happened after both the Gaya Session and Simon Commission.

Option 4: Gandhi-Irwin