The Battle of Plassey was a significant event in Indian history that took place in 1757. It was fought between the forces of the East India Company and the Nawab of Bengal. The question asks about the Nawab of Bengal during the Battle of Plassey. Option 1, Mir Jafar, and option 2, Mir Qasim, were both subsequent Nawabs of Bengal, but they were not in power during the Battle of Plassey. Option 3, Siraj-ud-duala, is the correct answer as he was the Nawab of Bengal at the time of the battle. He was young and inexperienced, and his defeat in the battle marked the beginning of British control over Bengal. With this victory, the East India Company established its dominance in India and laid the foundations of British colonial rule. Option 4, None of these, is incorrect as the Nawab of Bengal during the Battle of Plassey was indeed Siraj-ud-duala.