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 A)impertinent is correct as the word impertinent means not showing proper respect; rudeand the word rueful means expressing sorrow or regret, especially in a wry or humorous way.
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.