Find the compound ' A ' from the following reaction sequences. $\mathrm{A} \xrightarrow{\text { aqua-regia…
$\mathrm{A} \xrightarrow{\text { aqua-regia }} \mathrm{B} \xrightarrow[\text { (2) } \mathrm{AcOH}]{\text { (1) } \mathrm{KNO}_2 \mid \mathrm{NH}_4 \mathrm{OH}} \text { yellow ppt }$
- CoS
- ZnS
- NiS
- MnS
Solution
$\begin{aligned} \mathrm{CoS}+\mathrm{HNO}_3+3 \mathrm{HCl} \rightarrow \mathrm{Co}^{2+} & +\mathrm{S} \downarrow+\mathrm{NOCl} \uparrow \\ & +2 \mathrm{Cl}^{-}+2 \mathrm{H}_2 \mathrm{O}\end{aligned}$
The above solution is neutralised with $\mathrm{NH}_4 \mathrm{OH}$.
To a neutral solution of $\mathrm{Co}^{2+}$, acetic acid and saturated solution of $\mathrm{KNO}_2$ are added which results in the formation of yellow precipitate of $\mathrm{K}_3\left[\mathrm{Co}\left(\mathrm{NO}_2\right)_6\right]$
$\mathrm{Co}^{2+}+7 \mathrm{NO}_2^{-}+2 \mathrm{H}^{+}+3 \mathrm{~K}^{+} \rightarrow \mathrm{K}_3\left[\mathrm{Co}\left(\mathrm{NO}_2\right)_6\right]+\mathrm{NO} \uparrow+\mathrm{H}_2 \mathrm{O}$
Asked in: JEE Main 2025 (24 Jan Shift 2)