Concept:In a series R-L-C circuit, resonance occurs when the inductive reactance and capacitive reactance cancel each other.Explanation:At resonance, XL=XC.So the total reactance becomes zero.The impedance is then purely resistive: Z=R.Since R is the smallest possible opposition in this circuit, the impedance is minimum.The circuit behaves as a purely resistive circuit.Answer:Impedance is minimum, i.e. option B.