In a p-n junction under equilibrium:

The correct answer is Option (3) → No net current flows

When a p-n junction forms, holes and electrons diffuse across it and leave a depletion layer whose electric field drives a drift current in the opposite direction. The diffusion current falls and the drift current grows until the two are equal; this is the equilibrium state.

Option (1) Diffusion current dominates — Incorrect. Diffusion dominates only at the start, while the junction is forming; at equilibrium it is balanced by drift.

Option (2) Drift current dominates — Incorrect. Drift grows only until it equals the diffusion current; it never exceeds it without a bias.

Option (3) No net current flows — Correct. The two currents are equal and opposite, so the net current across the junction is zero.

Option (4) Depending upon the semiconductor either diffusion current or drift current dominates. — Incorrect. The balance holds for every p-n junction at equilibrium, whatever the semiconductor.

NCERT (2026-27):
p-n Junction Formation – “… Initially, diffusion current is large and drift current is small. As the diffusion process continues, the space-charge regions on either side of the junction extend, thus increasing the electric field strength and hence drift current. This process continues until the diffusion current equals the drift current. Thus a p-n junction is formed. In a p-n junction under equilibrium there is no net current.”