Which substance has the lowest standard molar entropy at 25°c?

Full question:

First of all, bear in mind that this question is incomplete. Here is the full question:

Which substance has the lowest standard molar entropy at 25°C?

a)  N₂O₄(g)

b) He(g)

c) NO₂(g)

d) NO(g)

He has the lowest standard molar entropy (126.1 J/K.mol)

Explanation:

Standard entropy is the absolute  entropy of a substance at 1 atm and 25°C.

Helium is a monatomic  gas, which cannot execute rotational or vibrational motions, in contrast with the other gases of the list. We need to keep in mind that that the spinning motion of an atom about its  own axis does not constitute a rotational  motion because it does not displace the  position of the nucleus.

The lowest standard molar entropy at 25°c for this gases (in J/K.mol) is:

N₂O₄(g) : 304.3

He(g) : 126.1

NO₂(g):  240.46

NO(g): 210.6

a polar bond is formed when electrons are shared unevenly between atoms

atomic mass = 39

number of neutrons = 20

number of protons= 19

electronic configuration = 1s2 2s2 2p6 3s2 3p6 4s1

the number of electron in first shell = 2

number of electrons in n=3 shell = 8