Synonyms are words which have the same or nearly the same meaning in the same language.
Antonyms are words which have opposite meaning in comparison to the other.
Option B)simplicity is correct as the word affectation means behaviour, speech, or writing that is pretentious and designed to impressand the word simplicity means the quality or condition of being easy to understand or do. Both the words are opposite of each other.
The other options are not correct as they do not have the opposite meaning to the given word.