Question

Alkali metal from the following with least melting point is:

• A. Rb
• B. Na
• C. K
• D. Cs

Answer 1

The Correct Option is D

To determine which alkali metal has the least melting point, we need to understand the properties of alkali metals. Alkali metals belong to Group 1 of the periodic table and include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).

Alkali metals are known for their softness and low melting points, which generally decrease as we move down the group. This is because the atomic size increases, and the metallic bonding becomes weaker due to increased atomic radii and the decreased strength of the attractive forces between the metallic ions and the delocalized electrons.

Given options are: 

• Rb (Rubidium)
• Na (Sodium)
• K (Potassium)
• Cs (Cesium)

Let's consider the melting points of these alkali metals:

Element	Symbol	Melting Point (°C)
Sodium	Na	98
Potassium	K	63.5
Rubidium	Rb	39.3
Cesium	Cs	28.5

We can clearly see from the table that cesium (Cs) has the lowest melting point among the given options at 28.5°C.

Conclusion: The alkali metal with the least melting point from the given options is Cesium (Cs).