NEET 2021 Chemistry Question 52 Solution

Noble gases (Group 18) are monoatomic gases with stable closed-shell electronic configurations ($ns^2 np^6$, except He which has $1s^2$). Because they possess neither permanent electric dipole moments nor covalent bonds between atoms, the only attractive forces holding them together in condensed states are exceedingly weak London dispersion forces (induced dipole - induced dipole interactions).

Owing to the weakness of dispersion forces, very little thermal energy is required to overcome these interactions. Consequently, noble gases have extremely low melting and boiling points. Helium has the lowest boiling point of any known element at $4.2\text{ K}$ ($-268.95^\circ\text{C}$). Therefore, Statement (2) asserting that noble gases have "very high melting and boiling points" is factually and scientifically incorrect.

- Statement 1: Noble gases are sparingly soluble in water due to weak dipole-induced dipole forces with polar water molecules (True). - Statement 3: Interatomic forces are indeed weak dispersion forces (True). - Statement 4: Noble gases possess stable octets; accepting an electron into the next higher quantum shell requires substantial energy input, resulting in large positive electron gain enthalpy ($\Delta_{\text{eg}}H > 0$) (True).