Which reagents are used for the identification of Group $IV$ cations?

When sodium nitroprusside is added to an alkaline solution containing sulfide ions,a ........ is obtained.

Consider the following reactions:
$X(aq.) \xrightarrow{K_4[Fe(CN)_6]}$ Chocolate brown ppt.
$X(aq.) \xrightarrow{AgNO_3}$ White ppt. (insoluble in dil. $HNO_3$)
Then $X$ will be:

In a solution containing $Hg^{2+}, Cd^{2+}, Sr^{2+}, Fe^{2+},$ and $Cu^{2+}$ ions in $0.3 \, M \, HCl$,which ions will precipitate upon the addition of $H_2S$?

$A$ precipitate of ....... would be obtained on adding $HCl$ to a solution of $(Sb_2S_3)$ in yellow ammonium sulphide.

When $MgSO_4$ reacts with $NH_4OH$ and $Na_2HPO_4$,it forms a white crystalline substance. What is the formula of that substance?