Royal Water, Acids Used to Dissolve King’s Metals
Puzzle 18 of Animals with Weird Names Hard Pack
Question is: Royal Water, Acids Used to Dissolve King’s Metals
and the answer is: AQUAREGIA
Word Meaning:
AQUA REGIA — (inorganic chemistry, archaic) A mixture of three parts concentrated hydrochloric acid to one part concentrated nitric acid, named for its ability to dissolve gold.
Definitions from Wiktionary.