The natural frequency of vibration of a massless rigid rod and small oscillations

Question

1. Considering massless rigid rod and small oscillations, the natural frequency (in rad/s) of vibration of the system shown in the figure is

(a)$\sqrt{\frac{400}{1}}$                         (b)$\sqrt{\frac{400}{2}}$                      (c)$\sqrt{\frac{400}{3}}$                         (d)$\sqrt{\frac{400}{4}}$