By which one of the following Acts was the Governor General of Bengal designated as the Governor General of India?

The Charter Act of 1833 was a pivotal piece of legislation in the constitutional history of British India. This Act significantly centralized the administration of British India. One of its most important provisions was the designation of the 'Governor-General of Bengal' as the 'Governor-General of India'. Lord William Bentinck, who was previously the Governor-General of Bengal, became the first Governor-General of India under this Act. The Act also vested him with all civil and military powers, further consolidating authority.

Other options:

The Regulating Act of 1773: Created the office of Governor-General of Bengal (first being Warren Hastings). The Pitt's India Act of 1784: Distinguished between commercial and political functions and established the Board of Control. The Charter Act of 1793: Extended the Company's trade monopoly for another 20 years and empowered the Governor-General to override his council's decisions.