What characterizes a perfect square?

A perfect square is characterized as a number whose positive square root is a whole number. This means that if you take the square root of a perfect square, the result will be an integer. For instance, the number 25 is a perfect square because its square root is 5, which is a whole number. Similarly, 36 is a perfect square since its square root is 6, also a whole number.

In contrast, other options do not accurately define perfect squares. While a perfect square can be expressed in fractional form, this is not relevant to the definition of a perfect square. The assertion that a perfect square cannot be factored is also incorrect; perfect squares can be factored (e.g., (a^2 = a \times a)). Lastly, a negative number's square root does not factor into the definition of perfect squares, as perfect squares are always non-negative by nature. Thus, defining perfect squares specifically in terms of having a whole number square root is both precise and accurate.