Discussion Forum



1)

The color of the X2 molecules of group 17 elements changes gradually from yellow to violet down the group. This is due to


A) decrease in $\pi^{*}-\sigma^{*}$ gap down the group

B) decrease in ionisation energy down the group

C) the physical state of $X_{2}$ at room temperature changes from gas to solid down the group

D) decreases in HOMO-LUMO gap down the group

Answer:

Option A,D

Explanation:

Color of halogen arises due to the transition from HOMO to LUMO   in the visible regions. On moving down a group, the difference in energy between HOMO  and LUMO decreases electronic transition occurs more easily and color intensity increases.