Answer: Diagram 4
Explanation: Diagram 1 represents a state in which particles are closely packed , thus cannot be a representation of gas.
Diagram 2 represents a state in which particles are loosely packed , thus can be a representation of gas.
Diagram 3 represents a state in which particles are closely packed , thus can be a representation of a solid.
Diagram 4 represents a state in which particles are loosely packed , thus can be a representation of gas. It also represents the particles in ionized form. Particles are existing as ions bearing positive and negative charges.