Why doesn’t the energy of a body doubles when temperature in degrees Celsius is doubled? I know that it doubles in case of kelvin scale.
You might find it interesting to read up on the differences between the different temperature scales. The kelvin scale effectively measures the vibration (average kinetic energy of molecules) so it makes sense that a doubling in the kelvin means a doubling in kinetic energy. On the other hand the Celsius scale is defined by the melting and boiling points of water (quite arbitrary).