Question: which one is not a perfect square?
Answer: Please note that all the perfect square numbers end with 0, 1, 4, 5, 6 or 9 but all the numbers with end with 0, 1, 4, 5, 6 or 9 are not perfect square numbers. Example, 11, 21, 51, 79, 76 etc. are the numbers which are not perfect square numbers.