The correct answer is option 4, the Treaty of Allahabad. The Treaty of Allahabad was signed in 1765 between the Mughal emperor Shah Alam II and the British East India Company. Under this treaty, the British company was granted the Diwani rights of Bengal, Bihar, and Orissa.

Diwani rights refer to the right to collect revenue and administer the civil justice system in a particular region. With the acquisition of the Diwani rights, the British Company gained significant control over the economic and administrative affairs of these regions. This treaty marked a turning point in the British company`s dominance and expansion in India.

Options 1, 2, and 3 are incorrect as they do not refer to the specific treaty that gave the British company the Diwani rights.