Answer
The molecules of the diatomic gas are rotating.
Work Step by Step
For a given transfer of energy, the temperature of the monatomic gas will increase more than the diatomic gas, because some of the added energy is transformed into the rotation of molecules in the diatomic gas.
This is why the pressure or volume increases more for a monatomic gas compared with a diatomic gas.
Therefore, the molecules of the diatomic gas are rotating.
