For an AC circuit to have current and voltage in phase, what condition must be met?

For an AC circuit to have current and voltage in phase, the condition that must be met is that the inductive reactance (XL) and capacitive reactance (XC) must be equal in magnitude, which leads to the sum of XL and XC being zero. This scenario occurs when the impedance is purely resistive, meaning that the net reactance in the circuit cancels out entirely.

When XL equals XC, the circuit is at resonance, resulting in the circuit being purely resistive, which allows the voltage and current to be in perfect phase alignment. This phase alignment means that both voltage and current reach their maximum and minimum values simultaneously, leading to efficient power transfer in the circuit.

In contrast, the other options suggest relationships that would not result in a current and voltage that are in phase. The second and third options relate more to specific configurations that would either introduce a phase shift or represent a condition where there is still some reactance present, thus not achieving the in-phase condition. Therefore, achieving the balance where XL equals XC and leads to their sum being zero ensures that the circuit behaves as required for current and voltage to be in phase.