Concept:Noble gases are non-polar, monoatomic elements. The only intermolecular forces acting between them are London dispersion forces, which scale with the polarizability of the atom.
Formula:$$ \text{Polarizability} \propto \text{Atomic Size/Number of Electrons} $$
Solution:- As we move down Group 18 in the periodic table (He, Ne, Ar, Kr, Xe, Rn), atomic radius and total electron count increase.
- A larger electron cloud is more diffuse and held less tightly by the nucleus, making it much easier to distort. This high polarizability creates stronger, more prominent temporary dipoles.
- Stronger London dispersion forces require more thermal energy to overcome.
- Among the given options, Krypton (Kr) is the largest atom located furthest down the group. Therefore, it possesses the strongest dispersion forces and the highest boiling point.
Why other options are incorrect:Helium is the smallest element with the tightest electron cloud, making it the least polarizable with the lowest boiling point of any known substance. Ne and Ar are intermediate.
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