An LCR series circuit its connected to a source of A.C. at resonance, the applied voltage and the current flowing through the circuit will have a phase difference of

$\pi$ $\frac{\pi}{2}$ $\frac{\pi}{4}$ 0

0

At Resonance $ X_C = X_L$ $\Rightarrow Z = R , Cos\phi = \frac{R}{Z} = 1 = Cos0$ $ \phi = 0$