Chlorine acts as a bleaching agent only in the presence of which of the following?

Chlorine is manufactured by

$POCl_3$ is prepared by the reaction of:
$(I)$ $P_4 + SO_2Cl_2 \to$
$(II)$ $P_4 + SOCl_2 \to$
$(III)$ $PCl_5 + SO_2 \to$
$(IV)$ $PCl_5 + C_2H_5OH \to$

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

Which among the following is the strongest acid?

$1$. $KClO_3 \xrightarrow{\Delta }$
$2$. $XeF_2 \xrightarrow{H_2O}$
$3$. $XeF_4 \xrightarrow{H_2O}$
$4$. $PbO_2 \xrightarrow{\Delta }$
$5$. $XeF_6 \xrightarrow{H_2O}$
In how many of the above processes,$O_2$ will be one of the products?