In an LCR series circuit, at resonance,

In an LCR series circuit, the total applied voltage $V$ is given by $V = \sqrt{V_R^2 + (V_L - V_C)^2}$.

At resonance, the inductive reactance equals the capacitive reactance (X_L = X_C$), which implies the voltage across the inductor equals the voltage across the capacitor (V_L = V_C$).

Substituting $V_L = V_C$ in the voltage equation, we get $V = \sqrt{V_R^2 + 0} = V_R$.

Thus, the voltage across the resistor $R$ is equal to the applied voltage.

Answer: the voltage across R equals to applied voltage.