Answer:
What is lighter than what it is made of?
The barber of New York shave all men in New York. No man living in New York is allowed to shave himself. The barber of Nee York lives in New York. Who shaves the barber ?
What contains zero calories, but if you consume it, you will probably gain weight?
Has feathers but can't fly. Rests on legs but can't walk.
I have rivers without water. Forests without trees. Mountains without rocks. Towns without houses.
What is so fragile that saying its name breaks it?