Nessler's reagent is

$M^{n+}(aq.) + KI \to X\downarrow \text{ (ppt.)}$ $\xrightarrow{Excess KI} \text{ppt. remains insoluble in excess } KI \text{ solution. Then cation } M^{n+}(aq.) \text{ can be}$

Match column-$I$ and column-$II$ with correct relation:

Column-$I$	Column-$II$
$(i)$ Blood like red colour	$(a)$ $Fe_4[Fe(CN)_6]_3$
$(ii)$ Sodium nitroprusside	$(b)$ $(NH_4)_2MoO_4$
$(iii)$ Ammonium molybdate	$(c)$ $[Fe(SCN)]^{2+}$
$(iv)$ Ferri-ferro cyanide	$(d)$ $Na_2[Fe(CN)_5NO]$

Which reagent is used in the qualitative analysis of Group $IV$ cations?

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:

Concentrated aqueous sodium hydroxide can separate a mixture of