Identify the alkali metal having the smallest atomic size from following.

Step-by-step solution

The alkali metals given in the options belong to Group 1 of the periodic table. As we move down a group, the number of electron shells increases, which leads to an increase in atomic size. The order of the given alkali metals from top to bottom in Group 1 is Sodium (Na), Potassium (K), Rubidium (Rb), and Caesium (Cs). Therefore, the order of their atomic sizes is Na Among the given options, Sodium has the smallest atomic size. Answer: Sodium