Match List I (Reagent/Test) with List II (Ion identified) based on...

Dimethylglyoxime reacts with $Ni^{2+}$ in an ammoniacal medium to form a rosy red precipitate of $Ni(DMG)_2$. This corresponds to test tube A. Thus, A $\rightarrow$ III.

Potassium chromate reacts with $Pb^{2+}$ to form a yellow precipitate of lead chromate, $PbCrO_4$. This corresponds to test tube B. Thus, B $\rightarrow$ I.

Sodium nitroprusside reacts with sulfide ions ($S^{2-}$) to form a purple-violet complex, $[Fe(CN)_5NOS]^{4-}$. This corresponds to test tube C. Thus, C $\rightarrow$ IV.

Potassium ferrocyanide reacts with $Cu^{2+}$ to form a chocolate brown precipitate of copper ferrocyanide, $Cu_2[Fe(CN)_6]$. This corresponds to test tube D. Thus, D $\rightarrow$ II.

The correct matching is A-III, B-I, C-IV, D-II.

Answer: A-III, B-I, C-IV, D-II