What is the appropriate classification for information that could critically impact national security?

The classification "Secret" is appropriate for information that, if disclosed, could cause serious damage to national security. This classification is often used for sensitive information related to military plans, intelligence operations, or diplomatic relations that require protection to ensure the safety and security of the nation.

The "Top Secret" classification denotes information that could cause exceptionally grave damage to national security, but in the context of information that could critically impact national security, "Secret" serves as a more fitting classification. "Confidential" is used for information that could cause damage but to a lesser degree. "Restricted" is not a recognized classification for national security information and generally pertains to internal information within an organization rather than classified information impacting national security. Therefore, "Secret" is the appropriate choice based on its specific implications for national security concerns.