Answer
$90^{\circ}$
Work Step by Step
Complement of $0^{\circ}$ will be another angle that terminal side needs to sweep in order to reach position y in figure 24 i.e. standard position of $90^{\circ}$.
Obviously it will be $90^{\circ}$.
Another way to find complement of an angle will be to subtract it from $90^{\circ}$.
Hence complement of $0^{\circ}$ = $90^{\circ}$- $0^{\circ}$ = $90^{\circ}$
