In a series resonant circuit at resonance, the circuit has:

In a series resonant circuit, the inductor and capacitor are connected end-to-end. At the resonant frequency, their individual reactances are exactly equal but opposite in phase, causing them to completely cancel each other out. With the reactive components effectively reducing to zero, the only remaining opposition to current flow is the natural, purely resistive component of the wire itself. Because there is virtually no reactance left to block the flow of alternating current at that specific frequency, a series resonant circuit presents a very low (minimum) impedance.