An external voltage is applied across a diode such that the n-side is…

The correct answer is Option (4) → (B) and (C) only

With the n-side positive and the p-side negative, the diode is reverse biased. The applied voltage is in the same direction as the barrier potential, so the effective barrier becomes \( V_0 + V \), and more majority carriers are pulled away from the junction.

(A) the barrier height decreases — Incorrect. This happens in forward bias.

(B) the barrier height increases — Correct. The barrier rises from \( V_0 \) to \( V_0 + V \).

(C) the depletion region widens — Correct. Electrons and holes move away from the junction, uncovering more ions, so the depletion region widens.

(D) the depletion region width decreases — Incorrect. This happens in forward bias.

(E) no change in barrier height — Incorrect. The barrier height increases.

NCERT (2026-27):
p-n Junction Diode Under Reverse Bias – “When an external voltage (V) is applied across the diode such that n-side is positive and p-side is negative, it is said to be reverse biased [Fig.14.15(a)]. The applied voltage mostly drops across the depletion region. The direction of applied voltage is same as the direction of barrier potential. As a result, the barrier height increases and the depletion region widens due to the change in the electric field.”