Reactive Yellow Element, Toxic as a Gas
This page is the CodyCross answer for the clue below from Top Secret, Group 2088, Puzzle 5 (Listening Post).
Question is: Reactive Yellow Element, Toxic as a Gas
and the answer is: FLUORINE
Word Meaning:
FLUORINE — (uncountable) The chemical element (symbol F) with an atomic number of 9. It is the lightest of the halogens, a pale yellow-green, highly reactive gas that attacks all metals.
Definitions from Wiktionary.