Question

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 ionization energy down the group
• C. decrease in $p^*-s^*$ gap down the group
• D. decrease in HOMO-LUMO gap down the group

Answer 1

Answer: (D)

decrease in HOMO-LUMO gap down the group

Answer 2

The colour of the $X_{2}$ molecules of group-11 elements changes gradually from yellow to violet down the group due to
(i) decrease in $\pi^{*}-\sigma^{*}$ gap down the group
(ii) decrease in HOMO-LUMO gap down the group