Neelam Sanjeeva Reddy was the 6th President of India}, and remains the only President elected unopposed in Indian history.
He was elected in 1977 after the Emergency period when all other candidates withdrew their nominations.
Clarification of other options:
(A) Dr. A.P.J. Abdul Kalam – Very popular, but was elected in a contested election in 2002.
(B) Smt. Droupadi Murmu – Contested against Yashwant Sinha in 2022.
(C) Dr. S. Radhakrishnan – Faced elections in 1962.
(D) Neelam Sanjeeva Reddy – Correct; elected unopposed in 1977.