The correct answer is (b), President.
The President of India is the custodian of the Consolidated Fund of India. The Consolidated Fund of India is a consolidated fund of all the money received by the Government of India from all sources, except loans raised by the Government. The President is also the supreme commander of the Indian Armed Forces.
The other options are incorrect. Parliament is the supreme legislative body of India. The Prime Minister is the head of the Union Government. The Finance Commission is a constitutional body that is appointed by the President to advise on the distribution of financial resources between the Centre and the States.