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The correct answer is: Argon has more neutrons, but Calcium has more protons.

The atomic number is the number of protons in an atom. In this case, argon has 18 protons and calcium 20.

The atomic mass (mass number) of an element is determined by the number of protons and the number of neutrons.

This means that the number of neutrons is atomic mass-atomic number. So, argon has 40-18=22 and calcium 40-20=20 neutrons.