According to the law of equipartition of energy, the Kinetic energy associated with each degree of freedom of a molecule is kT/2,

KE=

where k is Boltzmann constant,

T is absolute temperature.

f is the number of degrees of freedom

The number of degrees of freedom of a system is the minimum number of coordinates required to completely describe its position and orientation.

Now argon,

which is a monoatomic gas, can only translate along the x, y and z axes.

Hence, it has 3 degrees of freedom. Now, for a system,

total associated energy is:

Total energy of all the degrees of freedom,

Where

E = total energy,

f = number of degrees of freedom

k = Boltzmann constant = 1.38 x 10^-23m² kg s^-2 K^-1

T = absolute temperature (Kelvin)

For argon, f = 3. Therefore, which is minimum.

Options (b) and (c) are incorrect since they are diatomic and

have more than 3 degrees of freedom(translational and rotational degrees of freedom of 2 molecules).

Option (d) is incorrect since carbon dioxide is triatomic and has

more than 3 degrees of freedom(translational and rotational degrees of freedom of 3 molecules).

Hence, the correct answer is option (a).