Answer: i
Explanation:
It is imaginary, since if you try squaring numbers, ex: -1, 1,0,2 you always get a number bigger or equal to 0.
For years mathematicans argued weather the square root of -1 (or any negative number) should exist.
Then one day, a mathematician proposed a soulution, the square root of -1 could be i. Everyone liked that and so now the square root of -1 is i