Who initiated systematic surveys and reports documenting the customs and practices of different castes and tribes in an effort to better understand Indian society during the colonial period?

British administrative officials.

The correct answer is Option 1: British administrative officials.

Option 1: British administrative officials. Correct. British administrative officials undertook systematic surveys and prepared reports on the customs and practices of different castes and tribes. These studies formed an important part of the colonial effort to understand Indian society for administrative purposes.

Option 2: Indian social reformers. Incorrect. Indian social reformers worked towards eliminating social inequalities and reforming caste practices. However, they did not initiate the systematic colonial surveys and official reports on castes and tribes.

Option 3: Indian nationalist leaders. Incorrect. Nationalist leaders primarily focused on the struggle against colonial rule and social reform. The systematic documentation of caste customs and practices was undertaken by the colonial administration rather than nationalist leaders.

Option 4: Early Indian Census Commissioners after Independence. Incorrect. The surveys and reports referred to were prepared during the colonial period, long before Independence. They were part of the British administration's effort to understand and govern Indian society.