Which of these reactions is correct?

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

The colour of $Mg(OH)_2$ precipitate formed when it is precipitated in the presence of magneson reagent is

In the group analysis of cations, $Ba^{2+}$ and $Ca^{2+}$ are precipitated respectively as

$A$ salt with a few drops of conc. $HCl$ gives an apple green colour in a flame test. The group precipitate of the salt is dissolved in acetic acid and treated with $K_{2}CrO_{4}$ to give a yellow precipitate. When the sodium carbonate extract of the salt solution is heated with conc. $HNO_{3}$ and ammonium molybdate, it results in a canary yellow precipitate. The cation and anion present in the salt are respectively,

$A \xrightarrow{ K_4[Fe(CN)_6] } \text{Blue-white precipitate}$. Which ion is $A$?