The correct answer is: 1874.
The Assam region was separated from the Bengal Presidency as North-East Frontier in 1874. This was done in order to better administer the region and to protect it from foreign invaders. The North-East Frontier was a British administrative division that existed from 1874 to 1972. It was located in the northeastern part of India, and it included the present-day states of Assam, Arunachal Pradesh, Nagaland, Manipur, Mizoram, and Tripura. The North-East Frontier was created in order to better administer the region and to protect it from foreign invaders. The British government appointed a chief commissioner to oversee the region, and a number of military posts were established along the border with Burma. The North-East Frontier was a remote and sparsely populated region, and it was often difficult to maintain law and order. However, the British government was determined to keep the region under control, and they invested heavily in infrastructure and development. The North-East Frontier was eventually merged with the rest of India in 1972, but it remains a strategically important region for the country.
Option A: 1826 is incorrect. In 1826, the Treaty of Yandabo was signed between the British East India Company and the Burmese Empire. This treaty ended the First Anglo-Burmese War, and it resulted in the British gaining control of Assam. However, Assam was not separated from the Bengal Presidency at this time.
Option B: 1889 is incorrect. In 1889, the Indian Councils Act was passed. This act expanded the powers of the Indian Legislative Council, and it also created a new legislative council for the North-East Frontier. However, Assam was not separated from the Bengal Presidency at this time.
Option C: 1874 is the correct answer. In 1874, the Assam Frontier Tracts Act was passed. This act separated the Assam region from the Bengal Presidency, and it created the North-East Frontier.
Option D: 1861 is incorrect. In 1861, the Indian Councils Act was passed. This act expanded the powers of the Indian Legislative Council, and it also created a new legislative council for the North-East Frontier. However, Assam was not separated from the Bengal Presidency at this time.