Explanation:

The President of India is the head of state and the supreme commander of the Indian Armed Forces, while the Speaker of the Lok Sabha presides over the lower house of the Indian Parliament. * **Correct Option (B) Neelam Sanjiva Reddy:** Neelam Sanjiva Reddy holds the unique distinction of being the only person to have served as both the Speaker of the Lok Sabha and the President of India. He was the Speaker from 1967-1969 and again briefly in 1977 before being elected as the sixth President of India (1977-1982) unopposed. This makes his political journey particularly noteworthy. * **Incorrect Option (A) V.V. Giri:** V.V. Giri served as the fourth President of India (1969-1974) and was also a Vice President, but he never held the office of the Speaker of the Lok Sabha. His background was primarily in labor movements and as a Governor. * **Incorrect Option (C) Giani Zail Singh:** Giani Zail Singh served as the seventh President of India (1982-1987). Prior to becoming President, he was the Chief Minister of Punjab and a Union Home Minister, but he was never the Speaker of the Lok Sabha. * **Incorrect Option (D) S. Radhakrishnan:** S. Radhakrishnan was the second President of India (1962-1967) and the first Vice President of India. A distinguished philosopher and statesman, he did not serve as the Speaker of the Lok Sabha.