Pblock Elementsii Result Question 23
23. The colour of the $X _2$ molecules of group $17$ elements changes gradually from yellow to violet down the group. This is due to
(2017 Adv.)
(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
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Answer:
Correct Answer: 23. ( b,c )
Solution:
- Colour of halogen arises due to transition from HOMO to LUMO in the visible region. On moving down a group, the difference in energy between HOMO and LUMO decreases electronic transition occur more easily and colour intensity increases.
BETA
