Question

Which of the following is most polarised.
A. Kr
B. He
C. Ar
D. Xe

Answer 1

Hint: Polarisation is the property of polar molecules. Polar molecules contain positive and negative charges separated by a certain distance. Induced dipole-induced dipole attraction in noble gases causes the polarization of gas molecules.

Complete step-by-step solution:As we know, noble gases are inert in nature. They have no tendency to interact with outer elements. Thus, their charge cloud is considered to be symmetrical and not polarizable. But, however, they have a tendency to get polarize their electron cloud which leads to the generation of induced dipole and also the partial positive and negative charge. The dipole induced on one atom is able to induce a new dipole in the neighboring atom which is the formation of induced dipole-induced dipole interactions between noble gas molecules.
Now, we also know that the size of noble gas elements increases as we go down the group. The increasing order of size is given as He < Ne < Ar < Kr < Xe. With an increase in size, the electron cloud also increases. The influence of the nucleus over the outer electron cloud decreases and the possibility of distortion in the electron cloud of the atom increases. Therefore, the extent of polarization increases as the size of noble gases increases.
Hence, the extent of polarization increases as we go down the noble gas series. Xenon (Xe) gas is more polarized than other noble gases due to its larger size and its large electron cloud.

So, option D is correct

Additional Information:Helium gas is the least polarisable gas among noble gases due to its smaller size.

Note: According to fajan’s rule, the greater the size of an anion greater is the polarizability of the anion to distort its electron cloud. Also, the smaller size and larger charge on the cation have more tendency to distort the electron cloud of the anion.