Apples can float because 25% of their volume is air. Apples are less dense than water, so they float. An apple has the capacity to continue to absorb oxygen even after it is picked, which means it contains more air and is, therefore, less dense and has a lower water content.
This is also the reason why an apple is able to stay fresh longer than most fruits, because the apple still absorbs oxygen once picked. The apple in effect can breathe, which enables it to stay fresher longer.





