Which one of the following pairs of substances when mixed,produces chlorine gas at room temperature?

Acid strength of oxyacids of chlorine follows the order:

Identify a compound having highest thermal stability.

$A$ solid $A$ which has photographic effect reacts with the solution of a sodium salt $B$ to give a pale yellow precipitate $C$. The sodium salt $B$ on heating with concentrated $H_2SO_4$ gives brown vapours. Identify $A$,$B$,and $C$.

Oxygen reacts directly with all of the following elements except:

The correct statement$(s)$ about the oxoacids,$HClO_4$ and $HClO$,is(are):
$[A]$ $HClO_4$ is more acidic than $HClO$ because of the resonance stabilization of its anion.
$[B]$ $HClO_4$ is formed in the reaction between $Cl_2$ and $H_2O$.
$[C]$ The central atom in both $HClO_4$ and $HClO$ is $sp^3$ hybridized.
$[D]$ The conjugate base of $HClO_4$ is a weaker base than $H_2O$.