What classification marking is used for information that requires protection due to national security concerns?

The classification marking that is used for information requiring protection due to national security concerns is "Classified Markings: Confidential, Secret, or Top Secret." These classifications are established to protect sensitive information that, if disclosed without proper authorization, could harm national security.

Each of these categories—Confidential, Secret, and Top Secret—denotes a different level of sensitivity, where Confidential information could cause damage to national security, Secret information could cause serious damage, and Top Secret could cause exceptionally grave damage if disclosed. This structured hierarchy ensures that sensitive information is adequately safeguarded according to its level of risk.

In contrast, options like Restricted, Internal Use Only, and Public Domain do not pertain to national security classifications. "Restricted" typically refers to limitations on information for reasons other than national security, "Internal Use Only" is usually applied to private organizational information, and "Public Domain" indicates that the information is freely accessible to the public with no restrictions. Thus, only the classification markings for national security are appropriate for sensitive information.