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 C)defend is correct as the word defend means resist an attack made on (someone or something); protect from harm or dangerand the word implicate means show (someone) to be involved in a 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.