Which of the following is opposition to the flow of alternating current in a capacitor?
Why In an AC circuit a capacitor opposes current changes through capacitive reactance, Xc = 1/(2πfC), measured in ohms. Unlike resistance, reactance stores and returns energy instead of dissipating it as heat, and it changes with frequency: higher frequency or larger capacitance means less opposition. Inductors have reactance too (XL = 2πfL), so reactance is the general term for AC opposition from capacitance or inductance.
Watch out Conductance and admittance are the reciprocals of resistance and impedance, that is, measures of how easily current flows rather than opposition, and reluctance is opposition to magnetic flux in a magnetic circuit, not to current.
Reactance = the AC-only ohms of capacitors and inductors. Xc = 1/(2πfC).