Resonance in an LC circuit occurs when the magnitudes of inductive reactance and capacitive reactance are equal: $X_L=X_C⟹\omega L=\frac{1}{\omega C}$ ${\omega }^2=\frac{1}{LC}⟹{\omega }_0=\frac{1}{\sqrt{LC}}$ At this frequency, energy oscillates freely between the electric field of the capacitor and the magnetic field of the inductor.