The strongest reducing agent among the following is:

Why are halogens strong oxidising agents?

The reactions of $Cl_2$ gas with cold-dilute and hot-concentrated $NaOH$ in water give sodium salts of two (different) oxoacids of chlorine,$P$ and $Q$,respectively. The $Cl_2$ gas reacts with $SO_2$ gas,in presence of charcoal,to give a product $R$. $R$ reacts with white phosphorus to give a compound $S$. On hydrolysis,$S$ gives an oxoacid of phosphorus $T$.
$1.$ $P$ and $Q$,respectively,are the sodium salts of
$(A)$ hypochlorous and chloric acids
$(B)$ hypochlorous and chlorous acids
$(C)$ chloric and perchloric acids
$(D)$ chloric and hypochlorous acids
$2.$ $R$,$S$ and $T$,respectively,are
$(A)$ $SO_2Cl_2, PCl_5$ and $H_3PO_4$
$(B)$ $SO_2Cl_2, PCl_3$ and $H_3PO_3$
$(C)$ $SOCl_2, PCl_3$ and $H_3PO_2$
$(D)$ $SOCl_2, PCl_5$ and $H_3PO_4$
Give the answer for question $1$ and $2$.

Which of the following is the strongest reducing agent?

$A$ gas reacts with $CaO$,but not with $NaHCO_3$. The gas is

Identify the group of the periodic table that contains the element $Astatine$ $(At)$.