When $MgSO_4$ is treated with $NH_4OH$ and $Na_2HPO_4$,a white crystalline solid is formed. What is its formula?

Three different samples of a salt solution give the following test results: One sample gives a white precipitate with ammonia solution. One sample gives a white precipitate with dilute $NaCl$ solution. One sample gives a black precipitate with $H_2S$. Identify the salt.

$A$ mixture of chlorides of $Cu, Cd, Cr$ and $Fe$ was dissolved in water acidified with dil. $HCl$ and $H_2S$ gas was passed. It was filtered,and boiled later adding two drops of $HNO_3$. To this solution $NH_4Cl$ and $NH_4OH$ (or $NaOH$ in excess) were added. The filtrate shall give a test for :-

$A$ solution,when diluted with $H_2O$ and boiled,gives a white precipitate. On the addition of excess $NH_4Cl / NH_4OH$,the volume of the precipitate decreases,leaving behind a white gelatinous precipitate. Identify the precipitate which dissolves in $NH_4OH / NH_4Cl$.

Conc. $HNO_3$ is added before proceeding to test for group $III$ members. This is to

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