Calcium has an atomic number of 20 and an atomic mass (weight) of 40. therefore, we know that calcium has 20 protons 40 protons 20 electrons 40 electrons 20 neutrons (multiple choice)

It would have 20 protons, 20 neutrons, and 20 electrons. Protons and electrons are USUALLY (I say usually because of the different types of atoms) the same as the atomic number. To find neutrons you take the atomic mass minus the atomic number. 40-20=20