Which of the following figures shows the correct equipotential surfaces of a system of two positive charges?

Positive and negative point charges of equal magnitude are kept at $(0, 0, a/2)$ and $(0, 0, -a/2)$,respectively. The work done by the electric field when another positive point charge is moved from $(-a, 0, 0)$ to $(0, a, 0)$ is

$A$ charge $+Q$ is placed at the centre of a circular path of radius $r$. The work done to bring a charge $+q$ from one end of the diameter to the other end of the circular path in the electric field produced by charge $+Q$ is $.......$

$A$ uniform electric field exists in the plane of the paper as shown. Here $A, B, C$, and $D$ are points on the circle. $V_{A}, V_{B}, V_{C}$, and $V_{D}$ are the potentials at those points respectively. Then:

Assertion $(A)$: In a region of constant potential,the electric field is zero and there can be no charge inside the region.
Reason $(R)$: According to Gauss's law,the charge inside the region should be zero if the electric field is zero.

Two point charges $-Q$ and $+Q / \sqrt{3}$ are placed in the $xy$-plane at the origin $(0,0)$ and a point $(2,0)$,respectively,as shown in the figure. This results in an equipotential circle of radius $R$ and potential $V = 0$ in the $xy$-plane with its center at $(b, 0)$. All lengths are measured in meters.
$(1)$ The value of $R$ is. . . . meter.
$(2)$ The value of $b$ is. . . . . .meter.