When a p-n junction is forward biased, then,

The correct answer is Option (2) → it lowers the height of the potential barrier.

In forward bias the applied voltage opposes the built-in potential of the junction, so the effective barrier height falls from \( V_0 \) to \( V_0 - V \).

Option (1) it reduces the majority carrier current. — Incorrect. A lower barrier lets many more majority carriers diffuse across the junction, so the majority carrier current increases.

Option (2) it lowers the height of the potential barrier. — Correct. The applied voltage acts against the barrier potential and lowers it.

Option (3) it raises the height of the potential barrier. — Incorrect. The barrier is raised in reverse bias, where the applied voltage adds to the built-in potential.

Option (4) it increases the width of the depletion region. — Incorrect. The depletion region becomes narrower in forward bias; it widens in reverse bias.

NCERT (2026-27):
p-n Junction Diode Under Forward Bias – “… The direction of the applied voltage (\( V \)) is opposite to the built-in potential \( V_0 \). As a result, the depletion layer width decreases and the barrier height is reduced [Fig. 14.13(b)]. The effective barrier height under forward bias is \( (V_0 - V) \).”