As the frequency of the ac voltage across a capacitor approaches zero, the capacitive reactance of that capacitor:. a. approaches zero.
b. approaches infinity.
c. approaches unity.
d. none of the above.

b. approaches infinity

Explanation:

Because Capacitive reactance is given as Xc = 1/ωC

So we can see that the value of capacitive reactance and therefore its overall impedance (in Ohms) decreases to zero as the frequency increases acting like a short circuit.

Same as the frequency approaches zero or DC, the capacitors reactance increases to infinity, acting like an open circuit which is why capacitors block DC