Which of the following sulfides is yellow in color?

Aqueous solution of which of the following cation gives a precipitate with potash alum?

Consider the following sequence of reactions:
$M^{2+}(aq.)$ $\xrightarrow{NH_4Cl(s) + (NH_4)_2CO_3 \, sol.} Q \downarrow$ $\xrightarrow[\text{Followed by addition of } (NH_4)_2C_2O_4]{CH_3COOH} R \downarrow$
Which of the following cations can form precipitate $Q$ but does not form precipitate $R$?

What is formed when calomel $(Hg_2Cl_2)$ reacts with $NH_4OH$?

$Pb(CH_3COO)_2$ gives a precipitate of which color with $H_2S$?

Reagents used for the qualitative estimation of $Ni^{+2}$ and $Cu^{+2}$ respectively are: