Number i

$\sqrt {2}$ is real number(irrational number, $\pm$ 1.414213562373095048801688724209698........)

$\sqrt {1}$ is a integer, 1 and -1.

$\sqrt {-1}$ is an imaginary number. (Its exact value isn't defined, so it is known as $i$ ).

$\sqrt {0}$ is only 0, so it is an integer.

$\sqrt {-2}$ is a imaginary number like $\sqrt{-1}, i.$ (It is also can be expressed like $\sqrt {2}i$ .)