51.Who presides over the joint session of both the Houses of Parliament ?

The correct answer is (b), Vice President.

The Vice President of India is the ex officio Chairman of the Rajya Sabha. In the event of a joint sitting of the two Houses of Parliament, the Vice President presides over the sitting.

The Speaker of the Lok Sabha presides over the sittings of the Lok Sabha. The Prime Minister is the head of the government and is not a member of either House of Parliament. The President of India is the head of state and is not a member of either House of Parliament.