Jamnaben Mange, 79, and her son, Ashok Mange, 40, were arrested after they poured kerosene on Ashok's 30-year-old wife and set her ablaze, Thane police spokesperson Sukhada Narkar said.
The incident happened at around 7pm Friday at Mange's house in Raghunath Nagar area of Wagle Estate, police said.
"The victim has suffered 70 per cent burn injuries and is currently being treated at a hospital. We have filed a case under section 498 (A) (cruelty on woman by husband or relative of husband) and other sections of the Indian Penal Code. Further investigations are underway," the official informed.
Police said that the incident happened when the woman, who had shifted to her parents' house in Ghatkopar following constant quarrels with her mother-in-law, had come to her husband's home to pick up some documents of her daughter.