Which one of the following halogens liberates oxygen when passed through hot concentrated $KOH$ solution?

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

In the following reaction,identify the nature of the product formed by the complete hydrolysis of the underlined atom at $R.T.$:
$\underline{I}OF_5 + 2H_2O \longrightarrow HIO_4 + 5HF$

Which of the following is useful in the preparation of chlorine?

Which of the following decreases down the halogen group?

Anhydrous ferric chloride is prepared by