Explanation:

According to Article 60 of the Constitution of India, every President and every person acting as President or discharging the functions of the President before entering upon office shall make and subscribe oath to the office. The oath inter alia includes the oath to preserve, protect and defend the constitution. In this sense, President takes oath as guardian of Indian Constitution. The oath is administered by Chief Justice of India or in his absence by the senior-most Judge of the Supreme Court available.