Eight charges (each $q$) are placed at the vertices of a regular cube of side $a.$ The electric potential energy of the configuration will be $U=12\times \frac{1}{4\pi {\epsilon }_0}·\frac{q^2}{a}\times x.$ Then $x$

In the figure, two points $\left(A\right)$ and $\left(B\right)$ are located within a region that contains an electric field. A negative charge is placed at $\left(A\right)$ and then moved to $\left(B\right).$ Does the potential energy of the system increase, decrease or remain same?

Two fixed solid spheres of charges $Q$ and $kQ$ are separated by a distance $6R.$ A charge $-q$ is to be projected along the line joining their centres, so that it can reach the surface of other solid sphere of charge $kQ.$

(i) If $k=4,$ find minimum velocity to be given.
(ii) If we do not want to give any velocity, what should be the minimum value of $k?$