Step 1: What the question asks.
We need the largest island in the world.
Step 2: Island versus continent.
An island is land fully surrounded by water. But very large landmasses like Australia are called continents, not islands. So Australia is left out of this contest.
Step 3: Remove Australia.
Even though water is all around Australia, it counts as a continent, so it is not the answer.
Step 4: Compare the rest.
Greenland covers about 2.16 million square kilometres. New Guinea and Borneo are big, but clearly smaller than Greenland.
Step 5: The winner.
Greenland is the biggest piece of land that is still called an island.
Step 6: Conclusion.
So the world's largest island is Greenland.
Answer: Greenland