We have seen how the number of electrons and the number of protons affect the size of an atom or ion. However, we have not considered how the number of neutrons affects the size of an atom. Would you expect isotopes—for example, C-12 and C-13—to have different atomic radii?

(a) C-12 is larger than C-13.

(b) C-12 and C-13 are the same size.

(c) C-13 is larger than C-12.