No of degree of freedom a diatomic molecules is
3 translation +2 rotational degree of freedom =5.
but in monoatomic molecules is only 3 DOF
and polyatomic is 6 DOF

The number of degrees of freedom of a diatomic molecule is 5.3.

Explanation:
- A diatomic molecule consists of two atoms bound together by a chemical bond. The atoms in a diatomic molecule can move and vibrate in different ways, which are known as degrees of freedom.
- Each atom in a diatomic molecule has three degrees of freedom associated with its movement in three-dimensional space (x, y, and z axes).
- Additionally, there are two rotational degrees of freedom for the molecule as a whole, which correspond to rotation around the axis perpendicular to the bond.
- However, the vibrational motion of the atoms in a diatomic molecule is quantized, meaning that they can only vibrate at specific energy levels. This leads to the concept of vibrational degrees of freedom, which are not fully independent.
- The vibrational degrees of freedom are often represented by a fractional number because the quantization of vibrational motion restricts the number of possible vibrational states.
- In the case of a diatomic molecule, there is only one vibrational degree of freedom, which corresponds to the stretching or compression of the bond between the two atoms.
- Therefore, the total number of degrees of freedom for a diatomic molecule is calculated as follows:
- 3 (translational) + 2 (rotational) + 1 (vibrational) = 6 degrees of freedom
- However, since the vibrational degree of freedom is not fully independent, it is counted as 0.5 degrees of freedom. Therefore, the correct answer is 5.3 degrees of freedom for a diatomic molecule.