The Chromyl chloride test is performed for the confirmation of the presence of which of the following in a mixture?

The brown ring test is used to detect the presence of which of the following ions?

In the detection of $II$ group acid radical,the salt containing chloride is treated with concentrated sulphuric acid,the colourless gas is liberated. The name of the gas is

How do you account for the following observations?
$(a)$ Though alkaline potassium permanganate and acidic potassium permanganate both are used as oxidants,yet in the manufacture of benzoic acid from toluene,we use alcoholic potassium permanganate as an oxidant. Why? Write a balanced redox equation for the reaction.
$(b)$ When concentrated sulphuric acid is added to an inorganic mixture containing chloride,we get a colourless pungent-smelling gas $HCl$,but if the mixture contains bromide,then we get red vapours of bromine. Why?

$[X] + H_2SO_4 \to [Y]$ (a colourless gas with irritating smell).
$[Y] + K_2Cr_2O_7 + H_2SO_4 \to$ green solution.
$[X]$ and $[Y]$ are:

Choose the correct matching $:-$

Column-$I$	Column-$II$
$P$. $NaBr + \text{Conc. } H_2SO_4 \rightarrow$	$A$. Colourless gas
$Q$. $Na_2S + \text{dil. } HCl \rightarrow$	$B$. Brown colour
$R$. $NaNO_2 + \text{dil. } HCl \rightarrow$	$C$. Rotten egg smell
$S$. $NaNO_3 + \text{Conc. } H_2SO_4 \rightarrow$	$D$. Paramagnetic