Break medical and technical terms down to their Greek or Latin roots: 'anti-' means against, and '-biotic' comes from 'bios' meaning life. Therefore, it is always spelled with an 'o'.
Step 1: Check each word. Acrobatic, aerobatic, agnostic are correct. Step 2: Find misspelling. 'Antibiatic' should be 'antibiotic' (correct vowel is 'o' not 'a'). Answer: antibiatic (correct: antibiotic)