The correct answer is C. March, 1846 AD.
Maharaja Gulab Singh, the ruler of Jammu and Kashmir, acquired Kashmir in 1846 after the First Anglo-Sikh War. The war was fought between the British East India Company and the Sikh Empire, and resulted in the defeat of the Sikhs. As part of the peace treaty, the British gave the princely state of Kashmir to Gulab Singh in exchange for a payment of 7.5 million rupees.
Option A is incorrect because it is the year that Maharaja Ranjit Singh, the founder of the Sikh Empire, conquered Kashmir.
Option B is incorrect because it is the year that the Treaty of Amritsar was signed, which ended the First Anglo-Sikh War.
Option D is incorrect because it is the year that the Treaty of Lahore was signed, which ended the Second Anglo-Sikh War.