Which of the following is a volt?

$A$ conducting sphere of radius $R$ is given a charge $Q$ uniformly. The electric field and the electric potential at the centre of the sphere are respectively [$\epsilon_0 =$ permittivity of free space].

Three point charges $+Q$,$+2Q$,and $q$ are placed at the vertices of an equilateral triangle. The value of charge $q$ in terms of $Q$,so that the electrical potential energy of the system is zero,is given by:

Consider a sphere of radius $R$ with uniform charge density and total charge $Q$. The electrostatic potential distribution inside the sphere is given by $V(r) = \frac{Q}{4 \pi \varepsilon_{0} R} \left( a + b(r/R)^c \right)$. Note that the zero of potential is at infinity. The values of $(a, b, c)$ are

On moving a charge of $20 \; C$ by $2 \; cm$,$2 \; J$ of work is done. The potential difference between the points is (in $V$):

Four charges are arranged at the corners of a square $ABCD$ of side $d$,as shown in Figure.
$(a)$ Find the work required to put together this arrangement.
$(b)$ $A$ charge $q_{0}$ is brought to the centre $E$ of the square,the four charges being held fixed at its corners. How much extra work is needed to do this?