Identify the ion that has a smaller radius, Co²⁺ or Co³⁺. Justify your answer.

Co³⁺ has a smaller radius because Co³⁺ has fewer electrons and a higher effective nuclear charge compared to Co²⁺.

Co³⁺ has a smaller radius because Co³⁺ has more electrons and a lower effective nuclear charge compared to Co²⁺.

Co²⁺ has a smaller radius because Co²⁺ has more electrons and a lower effective nuclear charge compared to Co³⁺.