JEE Main · 2021 · 31 Aug 2021 · Shift 2 · Practical and Analytical Chemistry

In qualitative analysis cations are grouped by the reagent that precipitates them. ${\mathrm{Cu}}^{2+}$ precipitates as $\mathrm{CuS}$ with ${\mathrm{H}}_2\mathrm{S}$ in acidic medium (Group II-A). ${\mathrm{As}}^{3+}$ precipitates as $\mathrm{A}{\mathrm{s}}_2{\mathrm{S}}_3$ with ${\mathrm{H}}_2\mathrm{S}$ in acidic medium and belongs to the sulpho-salt sub-group II-B. ${\mathrm{Al}}^{3+}$ precipitates as $\mathrm{Al}(\mathrm{OH}{)}_3$ with $\mathrm{N}{\mathrm{H}}_4\mathrm{OH}$ in presence of $\mathrm{N}{\mathrm{H}}_4\mathrm{Cl}$ (Group III). ${\mathrm{Mn}}^{2+}$ precipitates as $\mathrm{MnS}$ with ${\mathrm{H}}_2\mathrm{S}$ in ammoniacal medium (Group IV). Thus ${\mathrm{Mn}}^{2+}$ is Group IV, ${\mathrm{As}}^{3+}$ is Group II-B, ${\mathrm{Cu}}^{2+}$ is Group II-A and ${\mathrm{Al}}^{3+}$ is Group III.