Balloon-Filling Gas
Puzzle 19 of ABBA Easy Pack
Question
Balloon-Filling Gas
Answer
HELIUM
Word Meaning:
HELIUM — (uncountable) The second-lightest chemical element (symbol He), with an atomic number of 2 and atomic weight of 4.002602, a colorless, odorless and inert noble gas.
Definitions from Wiktionary.