Explanation:

- Quiescent: This word means inactive, at rest, or dormant. It's used to describe something that's not in motion or active.

- Option 1: Dejected: Means sad or dispirited. This doesn't directly relate to activity levels, so it's not an antonym.

- Option 2: Active: This signifies movement, energy, or engagement. It is the direct opposite of quiescent because it implies being lively and dynamic.

- Correct Answer: Active

- Option 3: Peaceful: Means calm or tranquil. Similar to quiescent in that both imply a lack of disturbance.

- Option 4: Indifferent: Suggests a lack of interest or concern. It doesn't directly contrast with being inactive or quiescent.