He is (1)/ one of the tallest boy (2)/ in the class. (3)/ No error. (4)

Options

A. 1 He is
B. 2 one of the tallest boy
C. 3 in the class.
D. 4 No error.

Answer

2

Explanation

boys will replace boy because -
one of is followed by a Plural Noun/Pronoun
Look at the examples given below:
One of my fingers is hurting. One of them is a crook. Hence, one of the tallest boys is the right usage