Which of the following halogens can be purified by sublimation?

The following order is $NOT$ correct for: $HClO < HClO_2 < HClO_3 < HClO_4$

In the following reactions,products $(A)$ and $(B)$,respectively,are:
$6 NaOH + 3 Cl_{2} \xrightarrow{\text{hot and conc.}} (A) + \text{side products}$
$2 Ca(OH)_{2} + 2 Cl_{2} \xrightarrow{\text{dry}} (B) + \text{side products}$

$X_2$ is used in the refining of $Ti$ metal by the van Arkel method. $Y_2$ does not liberate $O_2$ from water and does not form $HY$ and $HOY$ with water. $X_2$ and $Y_2$ are respectively:

The reactive species in chlorine bleach is

What is the highest oxidation state exhibited by Group-$17$ elements?