Which one has the highest boiling point?
A.He
B.Ne
C.Kr
D.Xe

Hint: The melting and boiling points of noble gases are very low in comparison to those of other substances of comparable atomic and molecular masses.
This indicates that only weak van der Waals forces or weak London dispersion forces are present between the atoms of the noble gases in the liquid or the solid state.
The van der Waals force increases with the increase in the size of the atom, and therefore, in general, the boiling and melting points increase from He to Rn.
Helium boils at $2690^0C$.
Argon has larger mass than helium and has larger dispersion forces. Because of larger size the outer electrons are less tightly held in the larger atoms so that instantaneous dipoles are more easily induced
resulting in greater interaction between argon atoms. Therefore, its boiling point ($1860^0C$) is more than that of He.
Similarly, because of increased dispersion forces, the boiling and melting points of monatomic noble gases increase from helium to radon.

Complete step by step answer:
Among the noble gases, Xe has the highest boiling point.
The boiling points (in K) of He, Ne, Ar, Kr, Xe and Rn are 4.0, 27.0, 87.0, 121, 165.0 and 211 respectively.
On moving down the group, the atomic size increases,greater the size of the atom, greater will be the distortion of electron clouds of the atom and the stronger will be the dispersion force which will in turn increase boiling point of the group of the atoms.

So, the correct answer is Option D .

Note:
The temperature at which liquid vapour pressure equals atmospheric pressure is referred to as boiling point. The boiling point is defined as the temperature at which a liquid’s saturated vapour pressure equals the atmospheric pressure surrounding it.
The boiling point is important,As the boiling point of organic compounds provide valuable details about their physical and structural properties. Boiling point assists in the recognition and characterization of a compound. A liquid at higher pressure has a higher boiling point than when the atmospheric pressure of that liquid is lower.
Effects of boiling point of water
The surrounding pressures are the greatest determinant of the boiling point of a liquid. The air pressure in an open system is most definitely the atmosphere on earth. For instance, water reaches