In a forward biased p-n junction, the potential barrier

The correct answer is Option (1) → decreases

In forward bias, the p-side is connected to the positive terminal and the n-side to the negative terminal. So the applied voltage \( V \) acts opposite to the built-in potential \( V_0 \).

Option (1) decreases — Correct. The applied voltage works against the barrier, so the depletion layer becomes thinner and the barrier height falls to \( V_0-V \).

Option (2) increases — Incorrect. The barrier rises to \( V_0+V \) only in reverse bias, where the applied voltage is in the same direction as the barrier potential.

Option (3) remains constant — Incorrect. The applied voltage drops mostly across the depletion region, so it changes the barrier directly. The barrier stays at \( V_0 \) only when no voltage is applied.

Option (4) becomes zero — Incorrect. The forward voltage only lowers the barrier to \( V_0-V \). A small forward voltage reduces it only slightly below its equilibrium value. The barrier does not vanish.

NCERT (2026-27):
p-n Junction Diode under Forward Bias – “… The direction of the applied voltage (V) is opposite to the built-in potential V₀. As a result, the depletion layer width decreases and the barrier height is reduced …. The effective barrier height under forward bias is (V₀ – V).”