Explanation:

- Indolent means showing an inclination to avoid exertion or activity; being habitually lazy.

- Option 1: Lazy – This is a synonym, not an antonym, as it also describes someone who is unwilling to work or use energy.

- Option 2: Unskilled – This does not relate directly to level of activity or exertion, but rather the absence of skills or proficiency.

- Option 3: Active – This is the most appropriate antonym, as it describes someone who is engaging in energetic activities or being busy.

- Option 4: Sluggish – This implies a slow movement or lack of energy, aligning more closely with being indolent rather than opposing it.