Q. Find the compound 'A' from the following reaction sequences. $A\xrightarrow{\text{aqua-regia}}B\xrightarrow[(2)\ AcOH]{(1)\ KNO_2|NH_4OH}$ yellow ppt
A) CoS
B) ZnS
C) NiS
D) MnS
Explanation
[Solution by Dr. Abubacker] CoS dissolves in aqua regia to give $Co^{2+}$ (B). With $KNO_2$/$NH_4OH$ followed by acetic acid, $Co^{2+}$ is oxidised and forms the yellow precipitate of potassium hexanitritocobaltate(III), $K_3[Co(NO_2)_6]$. Answer (1).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.