Answer is: b) protons and electrons the same mass.
a) protons and neutrons are located in nucleus of an atom. Mass number is sum of protons and neutrons.
b) Protons and neutrons have nearly the same mass, while electrons are much less massive.
c) protons have positive and electrons have negative charge.
d) neutral atoms contain the same number of protons, for example, fluorine atom has 9 protons and 9 electrons.
