When more heat is supplied, the atoms or molecules may be ionized. An electron may gain enough energy to escape its atom. This atom loses one electron and develops a net positive charge. It becomes an ion.
In a sufficiently heated gas, ionization happens many times, creating clouds of free electrons and ions. However, all the atoms are not necessarily ionized, and some of them may remain completely intact with no net charge.
“Ionized gas mixture, consisting of ions, electrons
and neutral atoms is called Plasma.”
It means that a plasma is a distinct state of matter containing a significant number of electrically charged particles a number sufficient to affect its electrical properties and behavior.