The work done to move a charge on an equipotential surface is

$S_1$ and $S_2$ are two equipotential surfaces on which the potentials are not equal. Which of the following statements is incorrect?

The figure shows lines of constant potential in a region where an electric field is present. The electric field at point $B$ is............

There is a uniform electric field of intensity $E$ as shown in the figure. How many labelled points have the same electric potential as the fully shaded point?

Assertion $(A):$ $A$ spherical equipotential surface is not possible for a point charge.
Reason $(R):$ $A$ spherical equipotential surface is possible inside a spherical capacitor.

As per the diagram,a point charge $+q$ is placed at the origin $O$. The work done in taking another point charge $-Q$ from point $A$ [coordinates $(0, a)$] to point $B$ [coordinates $(a, 0)$] along the straight path $AB$ is: