The correct option is C 23
There are 2n non perfect square numbers between the squares of the numbers n and n + 1.
The number between 52 and 62 = 2×5=10
The number between 62 and 72 = 2×6=12
The number between 52 and 72 is
10 + 12 = 22
There are 22 non perfect square numbers between 52 and 72.