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)meagre is correct as the word sumptuous means splendid and expensive-looking and the word meagre means of something provided or available) lacking in quantity or quality. 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.