The correct option is B repulsive
The word 'captivating' refers to being capable of attracting and holding interest.
Option A, hateful refers to arousing or filled with hate.
Option B, splendid refers to being magnificent and very impressive.
Option C, repulsive refers to arousing intense distaste or disgust.
Option D, obscene refers to offending against moral principles.
Thus, according to the meaning, the word 'repulsive' is the opposite of the word 'captivating'.