Which from following anions has lowest coagulating power for precipitation of positive sol?

Which of the following elements belongs to first group and fifth period of periodic table?

If $\mathrm{E}^{\circ}$ cell for $\mathrm{Cd}_{(\mathrm{s})}\left|\mathrm{Cd}_{(\mathrm{IM})}^{2+} \square \mathrm{Ag}_{(1 \mathrm{M})}^{+}\right| \mathrm{Ag}_{(\mathrm{s})}$ is 1.2 V . What is the emf of the cell at $25^{\circ} \mathrm{C}$ ?

Identify a zero dimensional nano structure from following