Which Contributes More to an Atom's Mass: Electrons or Protons

Multiple Choice

Which contributes more to an atom's mass: electrons or protons? Which contributes more to an atom's size?

A) Protons contribute more to an atom's mass while electrons contribute more to its size.
B) Electrons contribute more to an atom's mass while protons contribute more to its size.
C) Protons contribute more to both the mass and size of an atom.
D) Electrons contribute more to both the mass and size of an atom.