The correct answer is: C. 1822.
Gulab Singh was declared as the Raja of Jammu by Ranjit Singh in 1822. He was a Dogra Rajput who served in the army of Ranjit Singh, the Maharaja of the Sikh Empire. In 1822, Ranjit Singh gave Gulab Singh the jagir (estate) of Jammu. Gulab Singh ruled Jammu until his death in 1857. He was succeeded by his son, Ranbir Singh.
Option A is incorrect because Gulab Singh was not declared as the Raja of Jammu in 1815. In 1815, he was still a young man and was not yet in the service of Ranjit Singh.
Option B is incorrect because Gulab Singh was not declared as the Raja of Jammu in 1860. In 1860, he was already dead.
Option D is incorrect because Gulab Singh was not declared as the Raja of Jammu in 1825. In 1825, he was already the Raja of Jammu.