Dear Student,
When gas is overheated: Heating of gas will increase the kinetic energy of gas molecules and they will collide with each other and it will increase the volume of gas as volume is directly proportional to the temperature. But, on extreme heating the colliding molecules will transfer to the next state of matter known has -plasma which is a super hot state in which the the gas becomes ionized and bond of molecules is decreased so that the electrons protons and neutrons are allowed to roam freely within a molecule.
Regards