(A) John F.Kennedy
(B) Barack Obama
(C) ** Theodore Roosevelt
(D) Bill Clinton
EXPLANATIONS BELOW
Concept note-1: -Roosevelt campaigned vigorously and the McKinley–Roosevelt ticket won a landslide victory based on a platform of victory, peace, and prosperity. Roosevelt assumed the presidency at age 42, and remains the youngest person to become president of the United States.
Concept note-2: -The youngest to become president by election was John F. Kennedy, who was inaugurated at age 43. The oldest person to assume the presidency was Joe Biden, the nation’s current president, who was inaugurated at age 78.
Concept note-3: -Presidential election of 1977 Reddy was elected unopposed, the only President to be elected thus, after being unanimously supported by all political parties including the opposition Congress party. At 64, he was the youngest person to be elected President of India until Droupadi Murmu was elected President in 2022.