Air Is Made Up of Mostly Nitrogen and This Gas
This page is the CodyCross answer for the clue below from Underground Worlds, Group 2163, Puzzle 1 (Lascaux Paintings).
Question is: Air Is Made Up of Mostly Nitrogen and This Gas
and the answer is: OXYGEN
Word Meaning:
OXYGEN — The chemical element (symbol O) with an atomic number of 8 and relative atomic mass of 15.9994. It is a colorless and odorless gas. Sometimes called elemental oxygen to distinguish it from molecular oxygen.
Definitions from Wiktionary.