In the series LCR circuit shown in figure the impedance is

Given parameters from the circuit:
Resistance, $R = 300\ \Omega$
Inductance, $L = 1\text{ H}$
Capacitance, $C = 20\ \mu\text{F} = 20 \times 10^{-6}\text{ F}$
Frequency of the AC source, $f = \dfrac{50}{\pi}\text{ Hz}$

The angular frequency $\omega$ is given by:
$\omega = 2\pi f = 2\pi \left(\dfrac{50}{\pi}\right) = 100\text{ rad/s}$

Inductive reactance, $X_L$:
$X_L = \omega L = 100 \times 1 = 100\ \Omega$

Capacitive reactance, $X_C$:
$X_C = \dfrac{1}{\omega C} = \dfrac{1}{100 \times 20 \times 10^{-6}} = \dfrac{1}{2 \times 10^{-3}} = 500\ \Omega$

The impedance $Z$ of the series LCR circuit is:
$Z = \sqrt{R^2 + (X_C - X_L)^2}$

Substituting the values:
$Z = \sqrt{300^2 + (500 - 100)^2}$
$Z = \sqrt{300^2 + 400^2}$
$Z = \sqrt{90000 + 160000}$
$Z = \sqrt{250000} = 500\ \Omega$

Answer: $500\,\Omega$