What type of round is used to signal or mark an area during night operations?

The correct answer is illumination rounds, which are specifically designed to provide light in a given area during nighttime operations. These rounds help to illuminate the battlefield, allowing soldiers to see obstacles, enemy positions, or other critical features that might otherwise remain hidden in darkness. Using illumination rounds enhances the situational awareness of the troops and can assist in coordinating movements and actions during night missions.

In contrast, high explosive rounds are more focused on delivering a destructive payload to targets rather than providing visibility. Smoke rounds are utilized for obscuring vision or marking, but they do not provide the illumination needed for visibility at night. Armor-piercing rounds are designed to penetrate armor and are not relevant for marking or signaling purposes in night operations. Thus, illumination rounds are the appropriate choice for enhancing visibility in low-light conditions.