a
The ortho and para isomers can be separated by steam distillation. onitrophenol is steam volatile due to intramolecular hydrogen bonding while \(p\) nitrophenol is less volatile due to intermolecular hydrogen bonding which causes the association of molecules.

Intramolecular hydrogen bonding takes place in ortho-nitrophenol because of the \(NO _2\) and \(OH\) molecules close proximity to each other.