A 2-year-old boy was thrown to his death from the balcony of a seventh-floor apartment in Queens on Tuesday night by a distraught woman who had been living with his family, the authorities said.

The woman, whom the authorities identified as Xiao Aiu Cai, 53, had a confrontation with someone else in the apartment and  for unknown reasons  lashed out at the boy, grabbed him, ran onto the balcony and threw him from it about 8:35 p.m., the authorities said.

Richard A. Brown, the Queens district attorney, said at the scene that the woman had been fighting with her daughter just before she turned to the boy and threw him from the home.

He said that the woman had been on medication and was very depressed.

The woman was taken into custody and was expected to be charged with murder.