Which of the following is a negative effect of posting on social media during training events or real-world operations?

Posting on social media during training events or real-world operations can inadvertently lead to the dissemination of sensitive information, such as a unit's exact location. When users upload photos that have geotagging activated, the GPS coordinates embedded in the images can reveal where the photo was taken. This can compromise operational security and put personnel at risk, as adversaries can use this information to track movements or anticipate actions.

The other choices, such as increased teamwork and enhanced public relations, while potentially positive outcomes in some contexts, do not directly address the security risks associated with sharing location-based information online. Improved communication may occur in informal settings, but it fails to mitigate the negative security implications that can arise from geotagged content. Therefore, the correct answer highlights a critical negative effect that must be managed to ensure the safety and effectiveness of military operations.