Option 1: Gyani Zail Singh is not the correct answer. He served as the seventh President of India from 1982 to 1987, but he was not a Lok Sabha Speaker.

Option 2: VV. Giri is not the correct answer. He served as the fourth President of India from 1969 to 1974, but he was not a Lok Sabha Speaker.

Option 3: Neelam Sanjiva Reddy is the correct answer. He is the only Lok Sabha Speaker to have become the President of India. He served as the sixth President of India from 1977 to 1982. Reddy was also the youngest Speaker of the Lok Sabha, serving from 1967 to 1969.

Option 4: K.R. Narayanan is not the correct answer. He served as the tenth President of India from 1997 to 2002, but he was not a Lok Sabha Speaker.

In conclusion, the correct answer is option 3, Neelam Sanjiva Reddy, who is the only Lok Sabha Speaker to have become the President of India.