Salt Analysis

$$ \begin{aligned} &\text { Find the compound ' } \mathrm{A} \text { ' from the following reaction sequences. }\\ &\mathrm{A} \xrightarrow{\text { aqua-regia }} \mathrm{B} \xrightarrow[\text { (2) } \mathrm{AcOH}]{\text { (1) } \mathrm{KNO}_2 \mid \mathrm{NH}_4 \mathrm{OH}} \text { yellow ppt } \end{aligned} $$