Fill in the blank with the most appropriate word. He is envious _____ his brother's success, and this makes him a sullen person.

Envious means jealous. It means feeling or showing discontented or resentful longing aroused by someone else's possessions, qualities, or luck.

Envious always takes the preposition of with it. Example: He was envious of his friend’s success.

Example: She was envious of her sister's new fashionable dress.

The correct answer is Option A) ‘of’. He is envious of his brother's success, and this makes him a sullen person.