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

The melting points of alkali metals decrease down the group. This trend is explained by the nature of metallic bonding:

• Metallic bonding arises from the electrostatic attraction between the positive metal ions and the sea of delocalized electrons.
• As the atomic size increases down the group, the outermost electron is held less strongly.
• This leads to weaker metallic bonding and, consequently, a lower melting point.

Melting Points of the Given Alkali Metals:

• Sodium (Na): 98°C
• Potassium (K): 64°C
• Rubidium (Rb): 39°C
• Cesium (Cs): 29°C

Observation:

Among the given alkali metals, cesium (Cs) is the largest atom, leading to the weakest metallic bonding and the lowest melting point.

Conclusion:

Final Answer: Cs has the least melting point.