1) The number of protons usually = the number of electrons in an atom.
2) If an atom changes its number of protons, it changes identity, such as 40K decaying to Ar.
3) Different isotopes of the same element may have different masses.
4) An atom's identity (whether it's hydrogen, helium, or something else) is determined by its atomic mass.
Hi! I have highlighted the correct... View the full answer