Which document serves as the original source for the categories of information that are eligible for classification?

The original source for the categories of information that are eligible for classification is Executive Order 13526. This executive order, issued by the President of the United States, establishes the framework for the classification of national security information and provides guidelines on how information should be classified, safeguarded, and declassified. It outlines the specific categories under which information can be classified, including those related to national defense and foreign relations. As such, this document is foundational for understanding the legal authority and criteria for information classification within the U.S. government, making it the correct choice in this context.