The equivalent capacitance between $A$ and $B$ is (in $\mu\, F$)

Five balls numbered $1$ to $5$ are suspended using separate threads. Pairs $(1,2), (2,4)$ and $(4,1)$ show electrostatic attraction while pairs $(2,3)$ and $(4,5)$ show repulsion. Therefore ball $1$ must be

Figures below show regular hexagons, with charges at the vertices, In which of the following cases the electric field at the centre is not zero.

Four dipoles having charge $ \pm e$ are placed inside a sphere. The total flux of ${\vec E}$ coming out of the sphere is 

For shown situation of two dipoles the nature of forces between them are

Two charges $q_1$ and $q_2$ are placed $30\,cm$ apart, as shown in the figure. A third charge $q_3$ is moved along the arc of a circle of radius $40\,cm$ from $C$ to $D$. The change in the potential energy of the $\frac{{{q_3}}}{{4\pi \,{ \in _0}}}k$ , where $k$ is