Which of the following best to account for the fact that the f- ion is smaller than the o2- ion?

a. f- has a larger nuclear mass than o2- has
b. f- has a larger nuclear charge than o2- has
c. f- has more electrons than o2- has
d. f- is more electronegative than o2- is
e. f- is more polarizable than o2- is

Option (B) is the correct answer.

Explanation:

Both oxygen and fluorine are period 2 elements and when we move across a period then there occurs a decrease in atomic size of the atoms. Hence, the atomic radius of a neutral fluorine atom is smaller than a neutral oxygen atom.

Moreover, atomic number of fluorine is 9 and it has higher nuclear charge due to which it will cause more attraction of electrons. As a result, size of a fluorine ion will be smaller.  

On the other hand, size of oxygen atom is larger and has small nuclear charge due to which attraction of electrons by its nucleus will not be strong enough. Hence, the size of will be larger.

Thus, we can conclude that the statement has a larger nuclear charge than has, is correct for the fact that the ion is smaller than the ion.