The atom of which element has an ionic radius smaller than its atomic radius?

a. n

b. s

c. br

d. rb

The answer to this question would be: d. rb

When forming ion, the cation will lose electron and anion will receive electron. The radius of atoms is determined by the electron, so when the cation lose electron their ionic form should have a smaller radius. In the question, Nitrogen, Sulfur, and Bromine is an anion, only Rubidium is the cation.