The alkali metals have relatively low melting point. Which one of the following alkali metals is expected to have the highest melting point?

Alkali metals (Group 1) exhibit a distinct periodic trend where their melting points decrease as one moves down the group from lithium to francium. This trend is primarily attributed to the weakening of metallic bonds. As the atomic radius increases down the group, the distance between the nucleus and the delocalized valence electrons increases, reducing the electrostatic attraction. Consequently, less thermal energy is required to overcome these forces and melt the metal. Among the options provided, Lithium (Li) is at the top of the group with the smallest atomic size and the strongest metallic bonding, resulting in the highest melting point of approximately 180.5°C. In contrast, sodium (97.8°C), potassium (63.5°C), and rubidium (39.3°C) have progressively lower melting points.