Answer
1 second
Work Step by Step
One complete revolution is equivalent to $360^{\circ}$
Time taken to rotate through $360^{\circ}$ = 4 seconds
Time taken to rotate through $1^{\circ}$ = $ \frac{4}{360} $ seconds
Time taken to rotate through $90^{\circ}$ = $ \frac{4}{360} \times 90 $ seconds
= 1 second
