Assertion: Electric field is aways directed perpendicular to an equipotential surface.
Reason: Equipotential surface is a surface on which at each point potential is same.

Explanation

Since pot. Diff. between two points A and B
=-line integral of electric field
or `dV=-int_(A)^(B)vecE.vec(dl)`
In a equipotential surface, dV=0
`therefore int_(A)^(B)vec(E).vec(dl)=0`
or `vec(E).vec(dl)=0`
or `vec(E) bot vec(dl)`