Which type of gas has free electrons and ions?

The correct answer is plasma, which is a state of matter distinct from solids, liquids, and gases. Plasma is formed at high temperatures or when sufficient energy is supplied to a gas, causing the electrons to become free from their atomic nuclei. This results in a collection of charged particles: free electrons and ions.

In plasma, these charged particles can conduct electricity and respond strongly to electromagnetic fields, which is why plasma can be found in phenomena like lightning, stars, and fluorescent lights. Unlike gases, where atoms or molecules remain neutral, plasma is characterized by this ionization process that leads to its unique properties and behaviors.

Other forms of matter listed in the choices do not exhibit the same characteristics. Liquid gas and vapor gas both refer to states of matter where molecular interactions are still intact, typically involving neutral atoms or molecules. Solid gas is not a recognized state of matter in scientific classification. Thus, plasma’s distinctive properties make it the only correct choice among those listed.