Theory:

A natural number is a perfect square if it is the square of other natural numbers.
Example:
36=36=6×6=6249=49=7×7=7225=25=5×5=52
 
Therefore here the \(36\), \(49\), and \(25\) are the perfect squares because these numbers are obtained, from squared by the exact whole numbers.
Not perfect squares:
 
If the square number ends with \(2\), \(3\), \(7\) and \(8\) will not be the perfect square.
Example:
Consider the numbers \(12, 23, 47, 88\) and take the square root; the result will not be the whole numbers.
 
12=3.464×3.464=(3.464)223=4.796×4.796=(4.796)247=6.856×6.856=(6.856)288=9.381×9.381=(9.381)2
From the above two explanations, you can see the difference that, perfect squares \(36, 49\) and \(25\) will be the square of whole numbers, but the other square numbers will not be the square of whole numbers.