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

On treating a solid salt $A$ with dil. $H_2SO_4$ and warming,reddish-brown fumes of gas $B$ are evolved. Addition of $C$ to the salt solution of $A$ followed by freshly prepared starch solution and acidification with acetic acid produces a blue colour. $C$ may contain:

$Fe$ (finely powdered) $+ HCl(dil.) \to P + Q\uparrow$. Compound $P$ does not precipitate with:

Which compound gives a black color with $NH_4OH$?

$A$ metal salt gives a yellow precipitate with potassium chromate in acetic acid and a white precipitate with dilute sulfuric acid,but it does not give a precipitate with sodium chloride or sodium iodide. What will be the composition of the white precipitate formed when sodium carbonate is added to the solution of this metal salt?

Which of the following pairs cannot be separated by passing $H_2S$ gas?