Explanation:

- Option 1 (1858): No census was held in 1858. The British had just taken direct control over India after the 1857 revolt, so there was no structured census this year.

- Option 2 (1881): This was the year of the first regular and synchronous decennial census across British India, which became a regular feature every 10 years after this.

- Option 3 (1872): There was a census in 1872, but it was not uniformly conducted across the country and was not decennial. It is sometimes called the first attempt at a census, but not a proper decennial one.

- Option 4 (1871): No census was undertaken in 1871. The earliest efforts for a census started in the early 1870s, but not on a pan-India scale.

The first decennial census, which gathered information including caste, was done in 1881 (Option 2).

Correct Answer: Option 2 (1881)