Which of the following is blocked by a capacitor?

The correct answer is Option (2) → dc

A capacitor has two plates with an insulator between them, so charge cannot cross from one plate to the other. Current flows in the circuit only while the plates are charging or discharging.

Option (1) ac — Incorrect. An ac source keeps reversing its voltage. The capacitor charges, discharges and charges again the other way in every cycle. So a current keeps flowing in the circuit.

Option (2) dc — Correct. With a dc source, current flows only for the short time needed to charge the plates. After that the current stays zero, so a steady dc cannot pass.

Option (3) Both ac and dc — Incorrect. Only the steady dc is stopped. An ac current keeps flowing because the capacitor charges and discharges again and again.

Option (4) Neither ac nor dc — Incorrect. A capacitor does stop a steady dc once it is fully charged.

NCERT (2026-27):
AC Voltage Applied to a Capacitor – “When a capacitor is connected to a voltage source in a dc circuit, current will flow for the short time required to charge the capacitor. … When the capacitor is fully charged, the current in the circuit falls to zero.”