The natural frequency of a rigid rod - spring arrangement

Question

1. A uniform rigid rod of mass m = 1kg and length L = 1 is hinged at its centre & laterally supported at one end by a spring of spring constant k = 300 N/m. The natural frequency $\omega _{n}$ in rad/s is                                            

(a) 10                              (b) 20                           (c) 30                              (d) 40