`(i)`
`(ii)` A surface where potential at every point is same called equipotential surface.
Because electric field goes on decreasing as we move away from charge. So, potential also decreases.
`(iii)` Let , electric field is tangent to equipotential surface, then work has to be done in moving a charge over surface but work done in moving a charge over an equipotential surface is zero so it contradicts our assumption.