An inductor of 0 . 5mH , a capacitor of 200μ F and a resistor of 2Ω...

Given here: $L = 0 . 5 \times {10}^{- 3}H$

$C = 200 \times {10}^{- 6}F$

$R = 2Ω$.

If current is in phase with emf, so this is the condition of resonance.

$f = {f}_{R} = \dfrac{1}{2\pi\sqrt{LC}} = \dfrac{1}{2 \times 3 . 14\sqrt{LC}}$

$f = \dfrac{1}{6 . 28\sqrt{0 . 5 \times {10}^{- 3} \times 200 \times {10}^{- 6}}} = 503 . 55Hz = 5 . 03 \times {10}^{2}Hz$