$A$ solution is prepared by mixing a concentrated solution of $Co(NO_3)_2$ with a concentrated solution of $NaNO_2$ in $50\%$ acetic acid. $A$ solution of a salt containing metal $M$ is added to the mixture, and a yellow precipitate is formed. Metal $M$ is:

When $H_2S$ gas is passed through the $HCl$ containing aqueous solutions of $CuCl_2$,$HgCl_2$,$BiCl_3$ and $CoCl_2$,which does not precipitate out?

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

$A$ salt '$A$' which gives a green flame with a Bunsen burner,on reaction with dil. $H_2SO_4$ produces gas $(2)$ and white turbidity $(Z)$. The saturated solution of gas $(2)$ on reaction with $H_2S$ gas produces '$Z$'. Then select the $CORRECT$ statement.

In which of the following is $NH_{3}$ not used?

An aqueous solution of a mixture of two inorganic salts,when treated with dilute $HCl$,gave a precipitate $(P)$ and a filtrate $(Q)$. The precipitate $P$ was found to dissolve in hot water. The filtrate $(Q)$ remained unchanged when treated with $H_2S$ in a dilute mineral acid medium. However,it gave a precipitate $(R)$ with $H_2S$ in an ammoniacal medium. The precipitate $R$ gave a coloured solution $(S)$ when treated with $H_2O_2$ in an aqueous $NaOH$ medium.
$1.$ The precipitate $P$ contains
$(A)$ $Pb^{2+}$ $(B)$ $Hg_2^{2+}$ $(C)$ $Ag^{+}$ $(D)$ $Hg^{2+}$
$2.$ The coloured solution $S$ contains
$(A)$ $Fe_2(SO_4)_3$ $(B)$ $CuSO_4$ $(C)$ $ZnSO_4$ $(D)$ $Na_2CrO_4$