Who among the following was elected President of India unopposed?

Dr. Neelam Sanjiva Reddy is the only President in the history of independent India to have been elected unopposed [t1][t2]. His election in July 1977 was necessitated by the untimely demise of President Fakhruddin Ali Ahmed [c1][t7]. Although Reddy had previously contested the 1969 presidential election as the official Congress candidate, he lost to V.V. Giri in a closely fought contest [c4][t1]. However, in 1977, following the Janata Party's rise to power, he was elected without any opposition after the nomination papers of other candidates were rejected [c1][t4]. While Dr. Rajendra Prasad served the longest tenure and Dr. S. Radhakrishnan served as the second President, both faced contests in their respective election cycles [t1][t8]. K.R. Narayanan was the first Dalit President but was also elected through a contested electoral process [t2].

Sources

1. [1] https://www.thehindu.com/news/national/sanjiva-reddy-only-president-elected-unopposed/article3529044.ece
2. [2] Rajiv Ahir. A Brief History of Modern India (2019 ed.). SPECTRUM. > Chapter 39: After Nehru... > New President of India > p. 705
3. [3] Rajiv Ahir. A Brief History of Modern India (2019 ed.). SPECTRUM. > Chapter 39: After Nehru... > Political Journey after Independence > p. 667