Asia
Australia, who is fully in the Eastern Hemisphere, does not border any other continents. Antarctica, who is partially in the Eastern Hemisphere, does not border any other continents as well.
Australia is an island continent separated from New Zealand by the Tasman Sea. Neither country shares a border with any other.
Antarctica is a continent that does not touch any other continents, as it is surrounded by the Southern Ocean. Australia is another continent that does not share a land border with any other continent.
Australia is an island continent. It is surrounded by sea, so doesn't share a land border with anyone.
Africa, Asia and Australia
Australia
Australia is the continent with the shortest land border, as it is completely surrounded by water with no land connections to other continents.
None, Australia is both a country and a continent. Its borders are therefore all oceanic.
The Indian Ocean is the western border of Australia.
Mt. Everest is located in Asia, specifically in the Himalayas on the border between Nepal and Tibet. The Mariana Trench is located in the Pacific Ocean and is closer to the continent of Asia and Australia than any other continent, but it is not part of any specific continent as it is underwater.
Antarctica is the continent that is not touching any other continent. It is isolated by the Southern Ocean.