On an equipotential surface:

The correct answer is Option (2) → the electric field is perpendicular to the surface

An equipotential surface is a surface on which every point has the same electric potential. Moving a charge \( q \) between two points on it needs no work, because \( W = q(V_{1} - V_{2}) = 0 \). If the field had a component along the surface, that component would do work on a charge moving along it; so the field has no component along the surface.

Option (1) work done by the electric field in moving a charge is positive — Incorrect. The potential difference is zero, so the work done is zero, not positive.

Option (2) the electric field is perpendicular to the surface — Correct. The electric field is normal to the equipotential surface at every point.

Option (3) electric field is tangential to the surface — Incorrect. A tangential field would do work on a charge moved along the surface, which is not possible when the potential is the same everywhere on it.

Option (4) work done by the electric field in moving a charge is negative — Incorrect. For the same reason as Option (1), the work done is zero, not negative.

NCERT (2026-27):
Equipotential Surfaces – “… This is true in general: for any charge configuration, equipotential surface through a point is normal to the electric field at that point. … But this is in contradiction to the definition of an equipotential surface: there is no potential difference between any two points on the surface and no work is required to move a test charge on the surface. The electric field must, therefore, be normal to the equipotential surface at every point.”