Question

which element will form the ion with the smallest ionic radius? rb k cs

Explanation:

Step1: Analyze the trend of ionic radius in a group

In a group of the periodic table, as we move down the group, the number of electron shells increases. For alkali metals (Group 1), when they form ions (all form \(M^{+}\) ions), the ionic radius increases with the increase in the number of electron shells.

Step2: Compare the positions of K, Rb and Cs

Potassium (\(K\)) is in the 4th period, Rubidium (\(Rb\)) is in the 5th period and Cesium (\(Cs\)) is in the 6th period. Since \(K\) has the least number of electron shells among the three when they form \(M^{+}\) ions.

Answer:

\(K\)