The term SOME ARE INERT can be broken down into two crossword solutions: GASES (5 letters). Gases are a state of matter that is composed of particles that are spread out and have no definite shape or volume. They are made up of molecules that are in constant motion and can move freely in any direction. Gases are also known for their ability to expand and fill any space available. Inert gases are a subset of gases that are chemically unreactive and do not form compounds with other elements. Examples of inert gases include helium, neon, argon, krypton, and xenon.