Find the Missing Exponent: Solving 0^□ = 0

To solve this problem, we need to understand how powers with a base of zero work. Typically, for any positive integer $n$, raising zero to that power results in zero, as follows:

• $0^n = 0$ for $n > 0$.

Therefore, to satisfy the equation $0^\square = 0$, the exponent $\square$ should be any positive integer. Hence, the missing number that makes the equation true is simply any positive integer.

Therefore, the correct answer is a (any number), which corresponds to any positive integer number.