In $Cr_2O_7^{2-}$,every $Cr$ is linked to

Thermal decomposition of a $Mn$ compound $(X)$ at $513 \ K$ results in compound $Y$,$MnO_2$ and a gaseous product. $MnO_2$ reacts with $NaCl$ and concentrated $H_2SO_4$ to give a pungent gas $Z$. Identify $X, Y$ and $Z$.

Match the aqueous solutions given in List-$I$ with their colors given in List-$II$:

List-$I$ (Aqueous solution of salt)	List-$II$ (Color)
$A$. $FeSO_4 \cdot 7H_2O$	$i$. Green
$B$. $NiCl_2 \cdot 4H_2O$	$ii$. Pale pink
$C$. $MnCl_2 \cdot 4H_2O$	$iii$. Blue
$D$. $CoCl_2 \cdot 6H_2O$	$iv$. Light green
$E$. $Cu_2Cl_2$	$v$. Pink
	$vi$. Colorless

The colour of the bead in the borax bead test is mainly due to the formation of:

How is sodium chromate converted into sodium dichromate in the manufacture of potassium dichromate from chromite ore?

The conductivity and appearance of $CrO_2$ are like metallic $Cu$.