Ok, I have 2 very different values for degree of freedom(DOF) of diatomic molecules arising due to the difference in the vibrational DOF of the diatomic molecules.
According to this DOF wiki page:-
Under Gas molecules section, one can see the Vibrational DOF of linear molecules, which is $3N-5$.
So, putting $N=2$, Vibrational DOF(Diatomic Molecule)=1 and so,
Total DOF(Diatomic Molecule)=6
In other wiki page namely, Molecular Vibration:-
A diatomic molecule has one normal mode of vibration.
But my textbook says otherwise. It's says the vibration contributes 2 to total DOF of diatomic molecule and so, Total DOF(Diatomic Molecule)=7
Here's the image:-
A VIDEO also says as per my textbook.
Look under the Syed Sumaid comment. There he explained why vibrational DOF of diatomic molecule should be 2 not 1(According to him).
I am not able to understand which one is delivering the right information.
Is it 7 DOF as per my book/that video or 6 DOF as per the wiki links I have given?