Six point charges, each of the same magnitude q , are arranged in...

Concise justification (one line per match): - A: $E=0 → p, r, s$. Each of these arrangements is point-symmetric about $M$ so the vector sum of electric fields cancels at $M$ : (p) alternating charges on a regular hexagon, (r) concentric rings with symmetric charge placement, (s) symmetrical rectangle with charges at corners/midpoints. - B: (V ≠ 0 $\rightarrow \mathrm{r}$), s. Potential is a scalar sum and need not cancel even if fields cancel; in ($r$) and ($s$) the positive and negative charges sit at different radii/positions so the net scalar potential at $M$ is nonzero. - C: (B=0 $\rightarrow \mathrm{p}, \mathrm{q}, \mathrm{t}$). When the whole system rotates about the shown axis the circulating currents from oppositely-signed charges cancel pairwise in these configurations, giving zero magnetic field at $M$. - ($\mathrm{D}$: \mu $\neq \mathrm{0} \rightarrow \mathrm{r}, \mathrm{s}$). In (r) and (s) the rotating charges produce unequal effective current loops (different radii or an unbalanced loop geometry), so a net magnetic moment remains. Hence choice (3).