Which of the following is the most active halogen?

Which of the following processes is used to produce chlorine by the oxidation of $HCl$?

The correct order of acidic strength of oxy-acids of chlorine is

Concentrated $H_2SO_4$ is not used to prepare $HBr$ from $KBr$ because it

Bromine is commercially prepared from sea water by displacement reaction:
$Cl_2 + 2Br^{-} (aq.) \to 2Cl^{-}(aq.) + Br_2$
$Br_2$ gas thus formed is dissolved into a solution of $Na_2CO_3$ and then pure $Br_2$ is obtained by treatment of the solution with:

State the electronic configurations of Group-$17$ elements.