Answer
$\omega \approx 0.181rad/s$
Work Step by Step
Angular frequency($\omega$) of the torsion pendulum is given by;
$\omega = \sqrt\frac{k}{I}$ where k is the torsion constant and I the moment of inertia about the torsion axis.
putting $k = \tau/\theta = 0.024 \frac{N.m}{rad}$
and $I = \frac{1}{2}mr^2 = 0.735 kg.m^2$ from the previous parts we get;
$\omega = \sqrt\frac{0.024}{0.735}rad/s \approx 0.181 rad/s$
