When the square root of a whole number is not another whole number, the result is an infinite decimal number that doesn't have periodicity.
For example, the number 2.151515... is infinite but has the value 15 repeating, so the number can be converted into a fraction.
But the square root of 5 is equal to 2.2360679..., and there is no pattern of numbers repeating.
In this case, where there is no periodic part in the infinite number, the number is an irrational number.
Therefore the correct option is A.
