Detailed Explanation:

Sardar Udham Singh assassinated Michael O'Dwyer on 13 March 1940 in London to avenge the Jallianwala Bagh massacre of 1919. O'Dwyer was the Lieutenant Governor of Punjab during the massacre and was held responsible by Udham Singh for sanctioning the brutal crackdown.

Curzon Wyllie was killed by Madan Lal Dhingra (1909), Saunders by Bhagat Singh (1928), and General Dyer (the actual executor at Jallianwala Bagh) died naturally in 1927.

Therefore, Michael O'Dwyer was assassinated by Sardar Udham Singh, making Option 2 the correct answer.