Option 1 states that the last Mauryan ruler was killed by his General. This means that the downfall of the Maurya empire was brought about by a betrayal from within. The General, who was loyal to the empire, turned against the ruler and killed him, effectively ending the Maurya dynasty.

Option 2 suggests that the Kanvas of Central India deposed the last Mauryan ruler. This implies that another ruling dynasty, the Kanvas, overthrew the Mauryan ruler and took control of the empire. However, this answer is not accurate as there is no historical evidence to support the claim that the Kanvas were responsible for the end of the Maurya empire.

Option 3 proposes that the last Mauryan ruler was killed in a battle with foreign invaders from the northwest. This implies that the downfall of the Maurya empire was a result of external forces. However, this answer is also not correct, as there is no historical evidence to suggest that the empire fell due to a battle with foreign invaders.

Option 4 suggests that the last Mauryan ruler had no heir and the throne was claimed by one of his powerful ministers. This implies that the empire fell into a power vacuum after the ruler`s death and one of