Most Important Selected Qs for JEE AdvancedChemistryp Block Elements (Group 15, 16, 17 & 18)
The colour of the X ₂ molecules of group 17 elements changes gradually from yellow to violet down the group. This is due to
Options
- AThe physical state of X ₂ at room temperature changes from gas to solid down the group
- BDecrease in HOMO-LUMO gap down the group
- CDecrease in ^*- ^* gap down the group
- DDecrease in ionization energy down the group
Correct answer
C. Decrease in ^*- ^* gap down the group
Step-by-step solution
Answer (B, C) The colours arise from the absorption of light on promoting an electron from the ground state to higher state. On descending the group, the energy levels become closer and gap between HOMO - LUMO decreases. HOMO is ^* LUMO is ^*