With which one of the following mountain tribes did the British first come into contact with after the grant of Diwani in the year 1765?

The correct answer is Option 2: Khasis.

Following the Grant of Diwani in 1765, the British East India Company acquired the right to collect revenues in Bengal, Bihar, and Odisha. This brought them to the Sylhet district (now in Bangladesh), which shared a direct border with the Khasi Hills. The British first came into contact with the Khasis primarily for trade, as the region was a major source of lime, silk, and iron.

• Khasis: They occupied the hills between the Jaintia and Garo ranges. Contact was established as early as 1765-1771 through Sylhet's administrators.
• Garos: British contact with the Garos occurred later, primarily towards the end of the 18th century as they moved further into the interior of the northeastern frontier.
• Kukis and Tipperahs: Interaction with these tribes happened much later, during the expansion into the Lushai Hills and the Chittagong Hill Tracts in the 19th century.

Thus, due to geographical proximity to the newly acquired Sylhet plains, the Khasis were the first mountain tribe encountered by the British post-1765.