Argon, Helium or Magnesium, for Example
Puzzle 2 of Recording an Album Medium Pack
Question is: Argon, Helium or Magnesium, for Example
and the answer is: ELEMENT
Word Meaning:
ELEMENT — One of the simplest or essential parts or principles of which anything consists, or upon which the constitution or fundamental powers of anything are based.
Definitions from Wiktionary.