The correct option is A The Chief Justice of India
The Chief Justice of India will discharge the functions of the President. Under Act No. 16 of 1969, in the event of the occurrence of vacancies in the office of the President and Vice President, by reason in each case of death, registration or removal , or otherwise the Chief Justice of India of the Supreme Court of India available shall discharge the functions of the President until a new President elected in accordance with the provisions of the constitution.