Which is the best reducing agent?

$Cl_2$ gas can be dried by passing it over ....

Chlorine reacts with sodium hydroxide under various conditions to give:

Among the following,the correct order of acidity is

How can you prepare $Cl_2$ from $HCl$ and $HCl$ from $Cl_2$? Write reactions only.

Among the following,the number of halide$(s)$ which is/are inert to hydrolysis is ..........
$(A)$ $BF_3$
$(B)$ $SiCl_4$
$(C)$ $PCl_5$
$(D)$ $SF_6$