The correct option is B Kindness
The word 'brutality' refers to great cruelty or savage physical violence.
Option A, violence refers to behaviour involving physical force intended to hurt, damage or kill someone.
Option B, kindness refers to the quality of being friendly, generous and considerate.
Option C, perfection refers to being flawless or faultless.
Option D, cruelty refers to behaviour which causes physical or mental harm to other.
Thus, according to the meaning, the word 'kindness' is the antonym of the word 'brutality'.