Question

Identify 'P' and 'Q' in the following reaction

• A. P = K$_2$[Cd(CN)$_4$], Q = CdS
• B. P = CdS, Q = K$_2$[Cd(CN)$_4$]
• C. P = Cd(NO$_3$)$_2$, Q = CdSO$_4$
• D. P = [Cd(OH$_2$)$_4$](NO$_3$)$_2$, Q = [Cd(NO$_3$)$_4$](NO$_3$)$_2$

Hint:

Using a simple frame or just bolding for the box Key Points:
Ligand Substitution: Stronger ligands (like CN$^-$) displace weaker ligands (like NH$_3$) from complex ions.
Cd$^{2+$ forms a stable tetracyano complex: [Cd(CN)$_4$]$^{2-$.
Precipitation: H$_2$S is used to precipitate metal sulfides. CdS is highly insoluble and yellow.
Even stable complexes can be decomposed if a very insoluble precipitate can be formed (like CdS).