The net magnetic flux through any closed surface is

The correct answer is Option (1) → Zero

Magnetic field lines form continuous closed loops, because isolated magnetic poles (monopoles) are not known to exist.

Option (1) Zero — Correct. Every field line that enters a closed surface also leaves it. So the inward and outward flux are equal in size, and the net flux is zero. This is Gauss’s law for magnetism.

Option (2) Always positive — Incorrect. A net outward flux would need field lines starting inside the surface, that is, an isolated north pole acting as a source of \( \vec{B} \).

Option (3) Always negative — Incorrect. A net inward flux would need field lines ending inside the surface, that is, an isolated south pole acting as a sink of \( \vec{B} \).

Option (4) Depends on the size of the surface — Incorrect. A larger surface is crossed by more lines. But each of them still enters and leaves it. So the net flux is zero for a closed surface of any size or shape.

NCERT (2026-27):
Magnetism and Gauss’s Law – “… Gauss’s law for magnetism is: The net magnetic flux through any closed surface is zero.”