The dimensional formula of the quantity ${\mathrm{RLC}}^2$ is [Here ‘R’ is resistance, L is inductance and C is capacitance]

RC is the time constant of RC circuit 

$\frac{1}{\sqrt{\mathrm{LC}}}$ is the angular frequency of L-C oscillator circuit.

$\therefore \left[\mathrm{RC}\right]={\mathrm{M}}^0{\mathrm{L}}^0{\mathrm{T}}^{1 }\mathrm{and} \left[\mathrm{LC}\right]={\mathrm{M}}^0{\mathrm{L}}^0{\mathrm{T}}^{2 }$

$\therefore \left[{\mathrm{RLC}}^2\right]={\mathrm{M}}^0{\mathrm{L}}^0{\mathrm{T}}^{3 }$