The total number of $Mn=O$ bonds in $Mn_2O_7$ is

$NaCl$ reacts with conc. $H_2SO_4$ and $K_2Cr_2O_7$ to give reddish fumes $(B)$,which react with $NaOH$ to give yellow solution $(C)$. $(B)$ and $(C)$ respectively are:

$Cr_2O_7^{2-} / H^{\oplus}$ $\xrightarrow[200^{\circ}C]{H_2O_2} 'X'$ $\xrightarrow{\text{On Standing}} 'Y'_{(aq. sol)}$
Select the correct option for $'X'$ and $'Y'$

$ \uparrow Y_{(g)} \xleftarrow{KI} CuSO_4 \xrightarrow{dil. H_2SO_4} X (\text{Blue colour}) $. $X$ and $Y$ are:

Which one of the following is lunar caustic?

Match List-$I$ with List-$II$:

List-$I$ (Transition metal/Compound/complex)	List-$II$ (Catalytic Role)
$A$. $V_2O_5$	$I$. Preparation of ammonia from $N_2/H_2$ mixture
$B$. $Fe$	$II$. Polymerisation of alkynes
$C$. $PdCl_2$	$III$. Preparation of $H_2SO_4$ from $SO_2$
$D$. $Ni$ complex	$IV$. Oxidation of ethyne to ethanal