Which element has the smallest atoms?
There is no completely correct answer to this question. The element which has the smallest atomic mass is Hydrogen (H), which has a proton and an electron. This could be taken as the element with the smallest atom. However, there are electron shells (where electrons move around) in an atom, and these are there even if they are not occupied, so the size of an atom of Hydrogen is the same as an atom of Bromine. This is why there are always the same amount of atoms in a defined space; and so, why different elements have such different densities
So, in respect to the size of the nucleus the answer is Hydrogen, but in respect to shells, there is no correct answer.
Hope it Helps! :D .