Which distinguishes an atom of one element from an atoms of a different element?

Which of the following elements would you expect to have the highest ionization energy value, and why? a. chlorine (cl), because it has a low effective nuclear charge and large radius b. fluorine (f), because it has a large radius and naturally forms a negative ion c. lithium (li), because it has a small radius and naturally forms a positive ion d. neon (ne), because it has a high effective nuclear charge and small radius