Hello,

It is very important to understand the concept of Degree of Freedom before you approach the question.

------- DOF or Degree of freedom in layman terms is basically no. Of ways in which a molecule can attain energy.

-------- So energy can be acquired by Translational motion, rotational motion and vibratory motion ( only at high temperatures).

-------- So, for a diatomic molecule and triatomic linear molecule like CO2 following DOF are associated with each form of motion:

• Translational motion - 3

• Rotational motion - 2

• Vibratory Motion - 2 (Only at High Temperature)

-------- Also energy associated with 1 DOF as per Maxwell's Law of equipartition of energy = 1/2KT ( K = Boltzmann Constant)

--------- Hence total Energy for CO2 molecule at normal temperature is 5/2KT.

I hope you find the answer helpful.

Thank you.