Question

Which of the following noble gas is the least polarizable?
(a)- Radon
(b)- Krypton
(c)- Xenon
(d)- Helium

Answer 1

Hint: The strength of the Polarizability of the element can be predicted by the size of the atom. As the size of the atom decreases, the strength of the polarizability decreases. So, from the options given above find the atom which has the smallest size.

Complete answer:
The degree to which an electron cloud can be bent by an electric field is known as polarizability. An atom, molecule, or ion is usually represented by an electron cloud. An electrode, for example, or a neighboring cation or anion may be the source of the electric field.
The genus to which an electron cloud belongs is polarizable if it is easily distorted. Usually, we use the term polarizability for ions, and the ions which have a larger size with negative charge have high polarizability while the ions which have a smaller size with positive charge have low polarizability.
So, the options given in the question are halogens which are group 18 elements. Since they do not form ions because they have a complete octet and do not combine with others.
Helium is the first element of group 18 as it is represented with He, and it has the smallest size. Helium has a smaller size, more closely bound valence electrons to the nucleus, and less polarizability.

Therefore, the correct answer is an option (d)- Helium.

Note:
The dielectric constant and, at high (optical) frequencies, the refractive index of a substance are determined by its polarizability. An atom or molecule's polarizability is defined as the ratio of its induced dipole moment to the local electric field.