\({S^{2 - }}\, + \,{[Fe{(CN)_5}NO]^{2 - }}\, \to \,\mathop {{{[Fe{{(CN)}_5}NOS]}^{4 - }}}\limits_{violet} \)
Thus \(S^{2-}\) and \(SO_3^{2-}\) can be distinguished by using both the given reagents.
$PCI _5( g ) \rightleftharpoons PCl _3( g )+ Cl _2( g )$