Presidents of India elected unopposed:
There have been two instances in the history of India where the President was elected unopposed. Let's discuss these instances in detail.

First instance:
The first time a President of India was elected unopposed was in 1952. Dr. Rajendra Prasad, who was also the first President of India, was elected without any opposition. This election took place after India became a Republic and adopted its Constitution. Dr. Rajendra Prasad was highly respected and had played a significant role in the Indian independence movement. Due to his immense popularity and the absence of any other candidates, he was elected unopposed.

Second instance:
The second instance of an unopposed election of the President of India occurred in 1977. Neelam Sanjiva Reddy, a prominent Indian politician, was elected unopposed as the President. This happened during the period of Emergency in India, which was a highly controversial time in the country's history. The ruling party at that time, the Indian National Congress, faced strong opposition, and the opposition parties decided not to nominate any candidate against Neelam Sanjiva Reddy. As a result, he became the President of India unopposed.

Conclusion:
In conclusion, there have been two Presidents of India who were elected unopposed. Dr. Rajendra Prasad in 1952 and Neelam Sanjiva Reddy in 1977 were both elected without any opposition. These instances highlight the immense popularity and respect these individuals commanded, leading to their unopposed elections as Presidents of India.