The correct option is C ambiguous
The word 'explicit' refers to being stated clearly and in detail.
Option A, wrong refers to being not correct and true.
Option B, inadequate refers to lacking the quantity or quality required.
Option C, no is used to give a negative response.
Option D, ambiguous refers to being open to more than one interpretation.
Thus, according to the meaning, the word 'ambiguous' is the opposite of the word 'explicit'.