i. Arrange the following in decreasing order of bond dissociation enthalpy
`F_(2) , Cl_(2) , Br_(2) , I_(2)`
ii. Bi does not form pπ-pπ bonds. Give reason for the observation.
iii.Electron gain enthalpy of oxygen is less negative than sulphur. Justify

Explanation

i. Arrange the following in decreasing order of bond dissociation enthalpy
`I_(2) < F_(2) < Br_(2) < Cl_(2)` ,
ii. Bi does not form pπ-pπ bonds as its atomic orbitals are large and diffuse so effective overlapping is not possible
iii.Due to small size of oxygen, it has greater elecrton electron repulsions