A class 11 student allegedly shot at and critically injured a girl, his friend and class 10 student, before shooting at himself in Sector 4C, police said on Thursday.
The girl, studying at a school in Delhi, was shot at in the head by the boy following a heated argument, they said.
The incident took place last evening near Vartalok society in Vasundhara when the duo was returning home on a scooty from a coaching centre, police said.
The boy also shot at himself with the licenced pistol, belonging to his father, they said.
They were rushed to a nearby hospital, police said, adding that the girl's condition was stated to be critical, while the boy was recapturing.
Assistant Superintendent of Police Anoop Singh said an FIR has been lodged against the boy following a complaint by the girl's uncle.
Police have recovered the pistol from the spot and have summoned the boy's father for questioning.