The correct answer is: C. Jaisimha.
Kalhana completed the Rajatarangini in 1148 CE, during the reign of King Jaisimha of Kashmir. The Rajatarangini is a chronicle of the history of Kashmir, from the time of the mythical king Parihasta Naga to the reign of King Harsha. It is one of the most important sources of information on the history of Kashmir.
Harsha was a Hindu king who ruled over the northern Indian subcontinent in the 7th century CE. He was a powerful and successful ruler, and he is considered to be one of the greatest kings in Indian history. However, he did not rule over Kashmir, and so he cannot have been the king during whose reign Kalhana completed the Rajatarangini.
Bhoja was a Hindu king who ruled over the Malwa region of India in the 10th century CE. He was a patron of the arts and sciences, and he is considered to be one of the greatest rulers in Indian history. However, he did not rule over Kashmir, and so he cannot have been the king during whose reign Kalhana completed the Rajatarangini.
Jaisimha was a Hindu king who ruled over Kashmir in the 12th century CE. He was a powerful and successful ruler, and he is considered to be one of the greatest kings in the history of Kashmir. He was the king during whose reign Kalhana completed the Rajatarangini.
Udairaj was a Hindu king who ruled over Kashmir in the 13th century CE. He was a weak and ineffective ruler, and he was eventually overthrown by his own son, Rinchana. He was not the king during whose reign Kalhana completed the Rajatarangini.