Question: A positively-charged hydrogen ion has a much smaller radius than a neutral hydrogen atom. Which best explains this difference?

  Options: 
 A. The nucleus is the least dense region of an atom.
 B. Electrons are located far from the nuclei of their atoms.
 C. Most of the volume of atoms is filled with the particles they contain.
 D. The repulsion of protons and neutrons keeps them on opposite ends of atoms.
Answer: B