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Reactance, a concept in AC (Alternating Current) circuits, is the opposition to the flow of alternating current due to capacitance or inductance. The unit of measurement for any type of resistance, including reactance, is the ohm.

In AC circuits, reactance can either be capacitive (due to capacitors) or inductive (due to inductors), and both types of reactance are expressed in ohms. This consistent use of ohms for reactance aligns with other electrical concepts where resistance, impedance, and reactance are all measured in the same unit, facilitating straightforward comparisons and calculations within electrical engineering and radio communications.

Other units listed, such as farad, volt, and henry, each measure different electrical properties. Farads are used for capacitance, volts measure electric potential or voltage, and henries measure inductance. Therefore, ohms is the correct unit for measuring reactance, ensuring a clear understanding of how it fits within the broader context of electrical and radio theory.