Explanation:

- Vain: Often refers to someone who is excessively proud of their appearance or achievements, or someone who is futile or useless.

- Option 1: Loyal: Means being faithful and committed to someone or something. This is not directly related to the meaning of "vain."

- Option 2: Modest: Describes someone who is humble and does not boast about their achievements. This is the direct opposite of "vain," which is about being excessively proud.

- Option 3: Unfair: This refers to a lack of justice or equality. It does not relate directly to the concept of vanity.

- Option 4: Energetic: Refers to someone full of energy and enthusiasm. It is unrelated to the idea of vanity.

- Correct Answer: Modest