NOIDA: A 21-year-old man allegedly jumped to his death from the fifth floor of a building located within the Bishrakh police station limits in Greater Noida on Saturday, police said.According to police, the deceased, identified as Sagar Yadav, was mentally unstable and had allegedly stabbed his mother following an altercation before taking the extreme step.Personnel from Bishrakh police station said Yadav, a resident of Radha Sky Garden Society, lived with his parents and younger brother."According to his family members, Sagar Yadav was not mentally sound. On Saturday, an altercation took place between him and his mother, during which he allegedly injured her with a knife. Subsequently, he jumped from the fifth-floor flat," police told PTI.Yadav was rushed to a nearby hospital, where doctors declared him dead.His mother is undergoing treatment at a hospital, police said.The body has been sent for postmortem after completion of legal formalities, and further investigation is underway, police added.(With agency inputs)