A salt solution gives a white gelatinous precipitate with aqueous ammonia that does not dissolve in excess; the precipitate dissolves in excess NaOH, and adding $\mathrm{NH}{}_4\mathrm{Cl}$ to that alkaline solution reprecipitates the white solid. The cation is

1. A$\mathrm{Zn}{}^{2+}$
2. B$\mathrm{Mg}{}^{2+}$
3. C$\mathrm{Cu}{}^{2+}$
4. D$\mathrm{Al}{}^{3+}$