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)exonerate is correct as the word exonerate means (of an official body) absolve (someone) from blame for a fault or wrongdoingand the word accuse means charge (someone) with an offence or crime.
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.