The correct option is B less than natural frequency Angular frequency of damped oscillation

\(\omega^{\prime}=\sqrt{\omega_0^2-\left(\frac{b}{2 m}\right)^2}\)

\(\Rightarrow \omega^{\prime} < \omega_0\)

Where natural angular frequency \(\omega_0=\sqrt{\frac{ k }{ m }}\)

Since frequency and angular frequency are related as,

\(\omega=2 \pi f\)

Hence, frequency of damped oscillation is less than natural frequency.