Final answer:
The most easterly point on mainland Australia is Cape Byron, located near Byron Bay in New South Wales.
Step-by-step explanation:
The question What is the most easterly point on mainland Australia? relates to the geographic extremities of the Australian mainland. The answer is (c) Cape Byron, which is situated at the easternmost point of the mainland, located near the town of Byron Bay in New South Wales. While Cape York and the Cape York Peninsula are quite far north and east, they are not the most easterly points. Wilsons Promontory is the southernmost point of the Australian mainland, and not the most easterly. Southeastern Australia extends from Queensland southwards to Victoria and Tasmania, but the most easterly point lies in New South Wales. Australasia includes not just Australia but also the island of Papua New Guinea and neighboring islands in the Pacific Ocean. However, for the context of this question, we are only concerned with the mainland of Australia itself.