What does the ability and opportunity to gain knowledge of classified information refer to?

The correct answer, national security eligibility, pertains to the assessment of an individual's background and circumstances to determine if they can be entrusted with access to classified information. National security eligibility evaluates factors such as loyalty, trustworthiness, and reliability, ensuring individuals upon whom sensitive information and access will be granted are of good character and have demonstrated a commitment to protecting national security interests.

Access control primarily focuses on the physical and administrative measures to protect classified information, generally excluding the assessment of the individual's qualifications or background for access. Security clearance refers to the formal designation that allows an individual to view classified information; however, having a security clearance does not inherently indicate the broader concept of national security eligibility. Classified access is more about the specific permissions granted to view classified information rather than the overall evaluation of an individual's suitability for such access. Hence, national security eligibility best captures the assessment related to one's ability and opportunity to gain knowledge of classified information.