Electric Potential Questions

An electric charge $10^{-3}\mu \text{C}$ is placed at the origin $(0,0)$ of $X-Y$ co-ordinate system. Two points $A$ and $B$ are situated at $(\sqrt{2},\sqrt{2})$ and $(2,0)$ respectively. The potential difference between the points $A$ and $B$ will be:

Two thin wire rings each having a radius $R$ are placed at a distance $d$ apart with their axes coinciding. The charges on the two rings are $+q$ and $-q$. The potential difference between the centres of the two rings is:

Two points $P$ and $Q$ are maintained at the potentials of $10\text{V}$ and $-4\text{V}$ respectively. The work done in moving $100$ electrons from $P$ to $Q$ is: