Precipitate of group $IV$ cations takes place when $H_2S$ is

Among the following cations,the number of cations which will give characteristic precipitate in their identification tests with $K_4[Fe(CN)_6]$ is :
$Cu^{2+}, Fe^{3+}, Ba^{2+}, Ca^{2+}, NH_4^{+}, Mg^{2+}, Zn^{2+}$

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

The compound that is white in color is

The solution of $BiCl_{3}$ in dil. $HCl$ when diluted with water,forms a white precipitate which is:

Identify the metal $M$ and the precipitate $Z$ in the following reaction sequence:
$MSO_4$ $\xrightarrow{NH_4OH} \downarrow X \text{ (white)}$ $\xrightarrow{NH_4OH \text{ (excess)}} Y$ $\xrightarrow{H_2S} \downarrow Z$