Question

Intramolecular hydrogen bonding takes place in ortho-nitrophenol but not in para- nitrophenol

Answer 1

in para nitrophenol the OH -OH functional group is in 1 and 4 position which is far to each other which does not capable to bond with the other hydrogen and oxygen of the functional group

Answer 2

Intramolecular hydrogen bonding takes place in ortho-nitrophenol because of the NO2 and OH molecules close proximity to each other and this disrupts possibility of molecular association.
In para-nitrophenol intramolecular hydrogen bonding takes place due to extensive hydrogen present in it.