Step 1: Test opposite meaning directly:
Worse means more bad, Better means more good, so the pair moves in opposite directions, which is the essence of antonyms.
Step 2: Rule out the rest:
The other three pairs are same-direction (synonym-like or same-polarity) pairs, not opposites.
Step 3: Final Answer:
Option (iii) 'Worse - Better' is the antonym pair.