Chlorine reacts with sodium hydroxide under various conditions to give:

$A$ radioactive element resembling iodine in properties is

$Cl_{2}O_{7}$ is the anhydride of

Write balanced chemical equations for the following:
$(i)$ $NaCl$ is heated with concentrated sulphuric acid $(H_{2}SO_{4})$ in the presence of manganese dioxide $(MnO_{2})$.
$(ii)$ Chlorine gas $(Cl_{2})$ is passed into an aqueous solution of sodium iodide $(NaI)$.

The gas evolved on heating $CaF_2$ and $SiO_2$ with concentrated $H_2SO_4$,on hydrolysis gives a white gelatinous precipitate. The precipitate is

Which of the following represents the correct order for oxidising power of the given species $ClO_4^{-}$,$BrO_4^{-}$,and $IO_4^{-}$?