Which of the following is opposition to the flow of alternating current in an inductor?
Why In an AC circuit an inductor opposes changes in current by generating a back EMF, and that frequency-dependent opposition is called reactance, specifically inductive reactance XL = 2*pi*f*L, measured in ohms. Unlike resistance it does not dissipate power; energy is stored in the magnetic field and returned to the circuit each cycle. Capacitors show the same kind of opposition, XC = 1/(2*pi*f*C).
Watch out Reluctance is the tempting one because it sounds magnetic, but it describes a magnetic circuit's opposition to magnetic flux, not current. Conductance and admittance are the reciprocals of resistance and impedance, so they measure how easily current flows, not opposition.
Reactance opposes AC in inductors and capacitors; reluctance opposes magnetic flux in a core. Words ending in -ance that start with 'ad-' or 'con-' mean easy flow.