Which of the following reactions would be incorrect?

$MnO_{2} + HCl \xrightarrow{\Delta} A_{(g)}$
$A_{(g)} + F_{2} (\text{excess}) \rightarrow B_{(g)}$
$B_{(l)} + U_{(s)} \rightarrow C_{(g)} + D_{(g)}$
The gases $A$,$B$,$C$ and $D$ are respectively

Chlorine was discovered by

The colour of the $X_2$ molecules of group $17$ elements changes gradually from yellow to violet down the group. This is due to
[$A$] the physical state of $X_2$ at room temperature changes from gas to solid down the group
[$B$] decrease in $HOMO-LUMO$ gap down the group
[$C$] decrease in $\pi^*-\sigma^*$ gap down the group
[$D$] decrease in ionization energy down the group

Which of the following statement$(s)$ regarding halogens is/are correct?

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