The word having opposite meaning as that of FRAIL is:
Synonyms are words which have the same or nearly the same meaning in the same language.
Antonyms are words which have the opposite meaning in comparison to the other.
Option B)strong is correct as the word frail means (of a person) weak and delicateand the word strong means having the power to move heavy weights or perform other physically demanding tasks Both the words are opposite of each other.
The other options are not correct as worried, nervous, wily are not the opposites of the word frail.