In a circuit, current will be maximum when reactance is minimum.
Reactance of an inductor of inductance $\mathrm{L}$ is,
$$
X_{: L}=2 \pi v L
$$
where $v$ is frequency of the AC circuit.


$$
\begin{aligned}
X_c &=\text { Reactance of the capacitive circuit } \\
&=\frac{1}{2 \pi f \mathrm{f}}
\end{aligned}
$$
On increasing frequency $v$, clearly $X_L$ increases and $X_C$ decreases
For a L-C-R circuit,
$\mathrm{Z}=$ Impedance of the circuit
$$
\begin{aligned}
&=\sqrt{\mathrm{R}^2+\left(\mathrm{X}_{\mathrm{L}}-\mathrm{X}_{\mathrm{C}}\right)^2} \\
&=\sqrt{\mathrm{R}^2+\left(2 \pi v \mathrm{~L}-\frac{1}{2 \pi v \mathrm{C}}\right)^2}
\end{aligned}
$$
As frequency $(v)$ increases, $Z$ decreases and at certain value of frequency know as resonant frequency $\left(v_0\right)$, impedance $Z$ is minimum that is $Z_{\min }=R$ current varies inversely with impedance and at $\mathrm{Z}_{\min }$ current is maximum.