Question

The component of electric field is parallel to an equipotential surface is zero, as the potential doesnot change in this direction, plz explain it briefly
  

Answer 1

Equipotential surface is always perpendicular(90°) to the direction of electric field. So the component of electric field along the equipotential surface is 0. 
Mathematically, 
component along the surface = E cos(90°) = E×0 = 0