Alkali metal from the following with least melting point is:
- Rb
- Na
- K
- Cs
The Correct Option is D
Solution and Explanation
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.
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