JEE Advanced 2017 Chemistry question

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

(A)the physical state of at room temperature changes from gas to solid down the group
(B)decrease in ionization energy down the group
(C)decrease in - gap down the groupCorrect
(D)decrease in HOMO-LUMO gap down the groupCorrect

Answer: (C),(D)

Solution

The colour of halogens arises from the excitation of an electron from the HOMO () to the LUMO (). Down the group the atoms become larger, the orbital overlap decreases and the - (HOMO-LUMO) gap decreases, so the absorbed light

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Question ID VK-026613