Final answer:
In DC circuits, capacitive reactance is infinite because once the capacitor is charged, there is no more voltage change to cause current to flow, effectively acting as an open circuit which blocks direct current.
Step-by-step explanation:
In a DC circuit, the capacitive reactance is considered infinite because a capacitor allows current to flow only as it charges and discharges. With direct current (DC), after an initial charge, there is no alternating voltage to continue changing the charge on the capacitor, making it act like an open circuit with no current flow. Therefore, the correct answer is (a) No flow of direct current, as once the capacitor is fully charged in a DC circuit, it will block any further current.
Capacitors and inductors behave differently in AC and DC circuits. Capacitors store energy in an electric field and are opposed to changes in voltage. In a DC circuit, once the capacitor is charged, there is no more change in voltage across it, and hence no current flows through it, which corresponds to an infinite reactance or impedance to current flow.