Which of the following is true?

The correct answer is Option (1) → Electric field lines are perpendicular to an equipotential surface.

An equipotential surface has the same potential at every point, so there is no potential difference between any two of its points.

Option (1) Electric field lines are perpendicular to an equipotential surface. — Correct. If the field had a component along the surface, work would be needed to move a charge along it. Then the points would be at different potentials. So the field is normal to the equipotential surface at every point.

Option (2) An infinite amount of work is done in moving a charge from one point to another on an equipotential surface. — Incorrect. The work done is the charge times the potential difference. This difference is zero between points of an equipotential surface, so no work is done.

Option (3) Electric field lines are parallel to an equipotential surface. — Incorrect. A field along the surface would push a charge along it and do work. Then the potential would change over the surface, and it would not be an equipotential surface.

NCERT (2026-27):
Equipotential Surfaces – “… Clearly, the electric field at every point is normal to the equipotential surface passing through that point. This is true in general: for any charge configuration, equipotential surface through a point is normal to the electric field at that point.”