by using smaller marbles to represent electrons by using two marbles to represent each neutron by using two differently colored marbles for protons by switching the colors of the marbles
I gave my students this multiple choice question: A model of an atom includes red marbles for electrons, green marbles for protons, and blue marbles for neutrons. All marbles have a radius of 2 cm. How could the model be changed to represent more properties of an atom?

Only one answer is correct among these 4 choices:
- by using smaller marbles to represent electrons
- by using two marbles to represent each neutron
- by using two differently colored marbles for protons
- by switching the colors of the marbles

Could you tell me which one is correct?

by using smaller marbles to represent electrons