Which of the integers 10, 11, 12, and 13 can be written as the sum of squares of four integers (allowing repetition)?

Correct option is D

Concept:
Lagrange's four square theorem - Lagrange's four square theorem, states that every natural number can be represented as a sum of four non - negative integer square.
Solution:
By using Lagrange's four square theorem all integers can be written as the sum of squares of four integers.
10 = 3² + 1²
11 = 3² + 1² + 1²
12 = 3² + 1² + 1² + 1²
13 = 3² + 2²
Hence, Option (d) is true.