Answer
$f=2Hz$
Work Step by Step
We know that,
$f=\frac{\omega}{2\pi}$.......................eq(1)
Also,
$\omega=\frac{2\pi}{T}=\frac{2\pi}{0.5}=4\pi\frac{rad}{s}$
We plug in the known values in eq(1) to obtain:
$f=\frac{4\pi}{2\pi}=2Hz$