Question

Which of the alkali metal is having least melting point?

• A. $K$
• B. $Na$
• C. $Rb$
• D. $Cs$

Answer 1

The correct option is D $Cs$

$\text{Melting point}:$

Melting point means the temperature at which a solid start to melt. Melting point of any element depends on the interatomic forces.

$\text{Melting point of alkali metal}:$

As we move down the alkali group atomic size increases i.e., the atomic size of Cesium $\left(Cs\right)$ is the highest and the atomic size of Sodium $\left(Na\right)$ is the lowest. We know as size of elements increase the binding energies of their atoms in the crystal lattice decrease. Also, the strength of metallic bonds decreases on moving down a group in the periodic table. This causes a decrease in the melting point.

Hence, among the given metals, $Cs$ is the largest and has the least melting point.

Therefore, the correct option is $\left(d\right)$

$\text{Final answer}:\left(d\right)Cs$