Apples float in water because they are twenty-five percent air.
Why it is true
The cellular structure of the apple contains air pockets that make its overall density lower than that of water, allowing them to float, which is the basis of the traditional game of bobbing for apples.
Source: Smithsonian
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.