The victim, identified as Rohit Yadav, 24, has suffered around 20 per cent burns on the neck and shoulder and his condition is stated to be stable.
The police, meanwhile, have denied the jilted lover theory.
Circle Officer (East area) M P Sharma said, "They were having an affair for a few months. A few days ago, Rohit stopped taking her calls. Upset at being ignored, Taiba Ahmad threw acid at him on Tuesday afternoon. After we got a call from the youth's family, we reached the spot. His family took him to a private hospital for treatment where he is recovering."
Taiba Ahmad has been booked under IPC section 326-A (acid attack).
Rohit's uncle Rakesh Kumar Yadav said both the families have known each other for long. "Her father is also very ashamed of what has happened and has apologised to us," said the uncle.
At a Lucknow hospital where Rohit is being treated, its director Dr Birendra Yadav said Rohit would be discharged in a day or two.
"He has only suffered superficial burns on his back and neck. The wounds will heal with help of medicines and ointment. He has suffered 20 per cent burns," said Dr Yadav.
The incident took place when Rohit was entering a dairy, owned by his family, at Gaunamau village under Maurawan police station area.
The accused was hiding behind a wall and threw acid on him as soon as he entered.
( With inputs from IANS )