Answer:
Western Australia
Step-by-step explanation:
The five main states on the mainland of Australia are the following:
1. Western Australia
2. Queensland
3. New South Wales
4. South Australia
5. Victoria.
While the territory on the mainland is known as Northern Territory.
However, of the five states on the Australian mainland, Western Mainland is the most western part.
Hence, in this case, the correct answer is WESTERN AUSTRALIA is the westernmost state in Australia.