Explanation:

- The Gandhi-Irwin Pact was a political agreement signed in 1931 between Mahatma Gandhi and the then Viceroy of India, Lord Irwin.

- Tej Bahadur Sapru mediated the negotiations. He was a prominent lawyer and politician. His moderating influence helped bridge the gap between the British government and Indian nationalists.

- Motilal Nehru was an important Congress leader, but he wasn't directly involved in the mediation of the Gandhi-Irwin Pact.

- Annie Besant was a theosophist and political activist who supported Indian self-rule, but not involved as a mediator in this context.

- Chintamani was also a political figure, but he played no significant role in mediating the pact.

So, your choice: Tej Bahadur Sapru is the mediator, and your answer is:

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