increasing atomic number from left to right increasing number of neutrons from left to right decreasing number of electrons from left to right decreasing atomic mass number from left to right
I gave my students this multiple choice question: Which statement best explains how periods on the periodic table are organized?

Only one answer is correct among these 4 choices:
- increasing atomic number from left to right
- increasing number of neutrons from left to right
- decreasing number of electrons from left to right
- decreasing atomic mass number from left to right

Could you tell me which one is correct?

increasing atomic number from left to right