As you move across a period, the atomic radii decreases. ... As you move across a period, electrons are added to the same energy level while protons are also being added. The concentration of more protons creates a higher effective nuclear charge.
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The atomic number of an element tells you the number of protons that an atom of the given element has.
An analogy is the closest way to compare something to another that may not be related so that would be my pick. If that’s not it I guess he could maybe be making an observational opinion about it? Good luck hope this helped. Analogy