Answer :
Answer: Option (a) is the correct answer.
Explanation:
As we know that entropy is the measure of degree of randomness. So, more is the mass of an atom more will be the electrons present in it and hence, more will be the repulsion between them.
As a result, more will be the entropy of the atom. For example, He, Ne, Ar, Kr are all group 18 elements. And, when we move down a group then there occurs an increase in atomic size of the atoms. Therefore, entropy also increases on moving down a group.
Thus, we can conclude that the correct order of increasing standard molar entropy for the noble gases is as follows.
He < Ne < Kr < Ar