Alkali metal from the following with least melting point is :

Solution

Chemistry ma’am · 3 steps

Bigger atom, weaker metallic bond, lower melting point, so go to the bottom of the group.

1. One electron each. Every alkali metal gives only one valence electron to the sea of electrons that holds the metal together. The metallic bonding is weak to begin with.
2. Size decides. Down the group the atomic size grows. The cation is larger and its single electron is farther away, so the attraction between the cations and the electron sea gets weaker. Less energy is then needed to melt the metal.

   Metal	Period	Melting point
   Na	3	371 K
   K	4	336 K
   Rb	5	312 K
   Cs	6	302 K, lowest

3. So. Caesium is the largest atom here and has the weakest metallic bonding, so Cs has the least melting point. It melts at about 29 °C, just above room temperature.

The idea to keep. In group 1, melting and boiling points fall steadily from Li to Cs. One bonding electron per atom and a growing atomic size make the metallic bond weaker as you go down.

Answer from the NTA final answer key. Solution by PrepWiser.