The correct answer is: a) 1872.
The first Census in Assam was conducted in 1872. It was conducted by the British government and was the first time that a census had been conducted in the region. The census recorded the population of Assam as being 1,924,437. The census also recorded the religious composition of the population, with Hindus making up the majority (68.4%), followed by Muslims (22.4%), Christians (8.1%), and others (1.1%).
The 1872 Census was a significant event in the history of Assam. It was the first time that the population of the region had been accurately recorded. The census also provided valuable information about the religious composition of the population, which was used by the British government to make decisions about the administration of the region.
The other options are incorrect because they are the years in which the subsequent censuses were conducted. The second Census in Assam was conducted in 1901, the third Census in 1921, and the fourth Census in 1951.