The correct answer is C. 1809 AD.
Maharaja Ranjit Singh acquired Kangra fort from Sansar Chand in 1809 AD. The fort was a major stronghold of the Katoch dynasty, and its capture was a significant victory for Ranjit Singh. The fort was located in a strategic location, and its capture gave Ranjit Singh control of a large area of territory. The fort was also a major source of revenue for Ranjit Singh, and its capture helped to finance his military campaigns.
Option A is incorrect because Kangra fort was not acquired by Ranjit Singh in 1805 AD. In 1805 AD, Ranjit Singh was still a young man, and he was not yet in a position to challenge the Katoch dynasty.
Option B is incorrect because Kangra fort was not acquired by Ranjit Singh in 1806 AD. In 1806 AD, Ranjit Singh was still consolidating his power in the Punjab, and he was not yet ready to launch a campaign against Kangra fort.
Option D is incorrect because Kangra fort was not acquired by Ranjit Singh in 1810 AD. In 1810 AD, Ranjit Singh was engaged in a war with the Afghans, and he did not have the resources to spare for a campaign against Kangra fort.