@ BMAD, your solutions do not count, because sqrt(-25), sqrt(-100), sqrt(-9), etc. are not integers.
A square (number) is the square of an integer and is necessarily nonnegative.
@ Grimbal, it is not a question of whether someone accepts 0 as a square (number). It is a fact.
Square numbers are the squares of integers. The phrase "in 3 unique ways" is ambiguous.