Question

How many states of matter exist?

Answer 1

At least `21`, possibly as many as `26` or more

Explanation:

Rather than enumerate them all, note that there are `4` classical states:

• Solid
• Liquid
• Gas

• Plasma

• `6` known non-classical states (e.g. liquid crystal)

• `8` known low temperature states (e.g. Bose-Einstein condensate a.k.a. BEC)
• `3` known high energy states (e.g. Degenerate matter (white dwarf and neutron star material))

Then there are `5` proposed states:

• Supersolid
• String-net liquid
• Superglass
• Dark matter
• Equilibrium gel

See https://en.wikipedia.org/wiki/State_of_matter for more details.