The correct option is D Incredible
The word 'plausible' refers to an argument or statement that seems reasonable or probable.
Option A, unacceptable refers to something not satisfactory or allowable.
Option B, incredible refers to something difficult to believe or extraordinary.
Option C, unlikely refers to something not likely to happen or improbable.
Option D, untrue refers to something not in accordance with fact or reality.
Thus, according to the meaning, the word 'incredible' is the farthest in meaning from the word 'plausible'.