Over which kind of surface can Gauss’s law be applied?

The correct answer is Option (1) → Any closed surface

Option (1) Any closed surface — Correct. Gauss’s law says that the electric flux through a closed surface equals \( q/\varepsilon_0 \), where \( q \) is the total charge enclosed by it. This holds for a closed surface of any shape or size.

Option (2) Only an open surface — Incorrect. An open surface does not enclose any region, so there is no enclosed charge for the law to use. The law is stated for closed surfaces.

Option (3) Only a plane surface — Incorrect. A plane surface is open and cannot enclose a charge. The surface used with Gauss’s law must be closed, such as a sphere or a closed cylinder.

Option (4) Only a closed surface that encloses no charge — Incorrect. With no charge inside, the law gives zero flux, but that is only one case. The law holds just as well when the surface encloses charge, and the flux is then \( q/\varepsilon_0 \).

NCERT (2026-27):
Gauss’s Law – “(i) Gauss’s law is true for any closed surface, no matter what its shape or size.”