JEE Advanced 2017 Paper 1

Electronic configuration of F2 molecule is σ1s2,σ1s*2,σ2s2,σ2s*2,σ2pz2,π2px2π2py2,π2px*2,π2py*2,σ2pz*2
⇒ Similar electronic configuration for other X2 molecules.
⇒ π*px and π*py are highest energy occupied molecular orbital (HUMO) and σ*pz is lowest energyunoccupied molecular orbital (LUMO).
⇒ Colour of X2 molecules of group 17 elements is due to transition of electrons from π* and σ*