Physics - EMI/AC Question with Solution | TestHub

The resonant frequency of an LCR circuit is given by $f=\frac{1}{2\pi \sqrt{LC}}$. It does not depend on the source frequency as well as the resistance of the circuit.

Therefore, to increase the resonating frequency product of $L$ and $C$ should decrease.

By joining another capacitor in series, the equivalent capacitor will decrease.

Hence, option C is correct option.