The correct option is C Bengal, Orissa and Bihar
The battle of Buxar was fought between the forces of the British East India Company and the combined army of an alliance of Indian states including Bengal, Awadh, and the Mughal Empire in the year 1764. The war came to an end by the "Treaty of Allahabad" in 1765. It granted the East India Company Diwani rights, or the right to collect taxes on behalf of the Emperor from the eastern province of Bengal, Bihar and Orissa.