In an LCR circuit  R = 100 ohm. When capacitance C is removed, the current lags behind the voltage by  . When inductance L is removed, the current leads the voltage by  . The impedance of the circuit is

When C is removed circuit becomes RL circuit hence            .....(i)When L is removed circuit becomes RC circuit hence            .....(ii)From equation (i) and (ii) we obtain XL = XC. This is the condition of resonance and in resonance Z = R = 100Ω