Sourav Khilari first sprinkled chili powder on the eyes of his mother Mousumi Khilari (45) and then strangulated her using a skipping rope, the sources said.
The woman managed to raise an alarm, following which their neighbours at Green Park under Belgharia police station reached there, broke open the door of their flat and found the woman lying dead.
The police came and arrested Sourav, the only child of Mousumi and her husband, a railway employee.
As his friends started receiving admit cards for HS Examination, Sourav thought now his parents would get to know that he had failed in the test examination, the police said.
His mother used to look after his studies, the police said adding Sourav's father was at office when the incident occurred.