An inductor of $0.5 \mu \mathrm{H}$, a capacitor of $200 \mu \mathrm{~F}$ and a resistor of $2 \Omega$ are connected in series with a 220 V ac source. If the current is in phase with the emf, the frequency of ac source will be $\_\_\_\_$ $\times 10^2 \mathrm{~Hz}$.
