The correct answer to the question "Who was the first Governor-General of Bengal?" is option 2, Warren Hastings.
Option 1, Robert Clive, was not the first Governor-General of Bengal. Although Clive held the position of Governor of Bengal in the 18th century and played a significant role in British colonial rule in India, he did not hold the title of Governor-General.
Option 3, William Bentinck, served as the Governor-General of Bengal from 1828 to 1835. He succeeded Lord Amherst.
Option 4, Cornwallis, served as the Governor-General of Bengal from 1786 to 1793. He was the first official Governor-General of Bengal under the Regulating Act of 1773, which established the role.
Therefore, the correct answer remains option 2, Warren Hastings, as he was the first Governor-General of Bengal, serving in the position from 1774 to 1785.