Is the square root of negative 4 rational or irrational?

The square root of -4 is the same thing as the square root of -1 times the square root of 4.  The square root of 4 is 2, but the square root is an imaginary number, i.  Since it is an imaginary number, it is indeterminate whether it is a rational or irrational (given current number theory) so the square root of negative 4 is neither rational nor irrational.  It is imaginary.

Sis less than or equal to 75 (bottom left)