Step 1: Understand the word "brittle".
"Brittle" means easily broken or fragile.
Step 2: Evaluate the options.
% Option
(1) STRONG: Correct antonym, as it implies durability.
% Option
(2) FRAIL: Synonym of brittle.
% Option
(3) FRAGILE: Synonym of brittle.
% Option
(4) DISMAL: Unrelated in meaning.