Final answer:
The Commonwealth Star is the official symbol that identifies Commonwealth property in Australia. It represents the unity of the states and territories of the nation. Australia's unique marsupials, such as the wallaby and echidna, are classified as endemic species, found only in Australia.
Step-by-step explanation:
The official symbol of Australia that identifies Commonwealth property is b. Commonwealth Star. Australia’s federation in 1901 created a commonwealth government, maintaining individual state distinctions while also establishing national symbols. The Commonwealth Star, also known as the Federation Star, is a key element of the Australian flag, representing the unity of the six original states and the territories of the Commonwealth of Australia.
Marsupials like the wallaby and the echidna are unique to Australia and are considered a. endemic species, meaning they are found exclusively in a particular area, in this case, Australia. These species are part of Australia’s rich biodiversity and are symbolically significant to the nation.