Gas Combined With Hydrogen to Make Ammonia
Puzzle 10 of Great Explorations Hard Pack
Question is: Gas Combined With Hydrogen to Make Ammonia
and the answer is: NITROGEN
Word Meaning:
NITROGEN — (uncountable) The chemical element with an atomic number of 7 and atomic weight of 14.0067. It is a colorless and odorless gas.
Definitions from Wiktionary.