How many letters does the top answer for “pertaining to, or designating, the highest oxygen acid, hbro4, of bromine.” have?

The most common answer is perbromic (9 letters).

Crossword clue: pertaining to, or designating, the highest oxygen acid, hbro4, of bromine.

1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

perbromic 9 letters web-def

Pertaining to, or designating, the highest oxygen acid, HBrO4, of bromine.