$MgSO_4$ on reaction with $NH_4OH$ and $Na_2HPO_4$ forms a white crystalline precipitate. What is its formula?

In the wet tests for detection of various cations by precipitation,$Ba^{2+}$ cations are detected by obtaining a precipitate of

Which of the following radicals will not be precipitated by passing $H_2S$ in a concentrated acid solution?

Which of the following statement$(s)$ is/are correct with reference to $Fe^{2+}$ and $Fe^{3+}$ ions?
$(1)$ $Fe^{3+}$ gives brown colour with potassium ferricyanide
$(2)$ $Fe^{2+}$ gives blue colour with potassium ferricyanide
$(3)$ $Fe^{3+}$ gives red colour with potassium thiocyanate
$(4)$ $Fe^{2+}$ gives brown colour with ammonium thiocyanate

The compound that is white in color is

$p$-Amino-$N,N$-dimethylaniline is added to a strongly acidic solution of $X$. The resulting solution is treated with a few drops of aqueous solution of $Y$ to yield blue coloration due to the formation of methylene blue. Treatment of the aqueous solution of $Y$ with the reagent potassium hexacyanoferrate$(II)$ leads to the formation of an intense blue precipitate. The precipitate dissolves on excess addition of the reagent. Similarly,treatment of the solution of $Y$ with the solution of potassium hexacyanoferrate$(III)$ leads to a brown coloration due to the formation of $Z$.
$1.$ The compound $X$ is
$(A)$ $NaNO_3$ $(B)$ $NaCl$ $(C)$ $Na_2SO_4$ $(D)$ $Na_2S$
$2.$ The compound $Y$ is
$(A)$ $MgCl_2$ $(B)$ $FeCl_2$ $(C)$ $FeCl_3$ $(D)$ $ZnCl_2$
$3.$ The compound $Z$ is
$(A)$ $Mg_2[Fe(CN)_6]$ $(B)$ $Fe[Fe(CN)_6]$
$(C)$ $Fe_4[Fe(CN)_6]_3$ $(D)$ $K_2Zn_3[Fe(CN)_6]_2$
Give the answer for questions $1, 2$ and $3$.