Correct option is D
Logic: Smart and Intelligent are the synonyms.
from the given options
(a) Liable : Accountable – Liable and Accountable are the synonyms.
(b) Modest : Humble – Modest and Humble are the synonyms.
(c) Nimble : Sluggish – Nimble and Sluggish are the antonyms.
(d) Outbreak : Eruption – Outbreak and Eruption are the synonyms.
So, only the words in (3) does not have the same relationship as the given words.
Thus, the correct answer is option (d).