The correct option is C 2n
The squares of n and (n + 1) are n2 and ( n+1)2.
So, the number of non-perfect square numbers between these two squares is
( n+1)2− n2−1
( e.g. the number of natural numbers between 4 and 7 is 7 - 4 - 1 = 2)
= n2+2n+1− n2−1
= 2n
So, the correct option is B.