Final answer:
Most information in system of records falls under FOIA exemption 6, which is Invasion of personal privacy.
Step-by-step explanation:
The most common Freedom of Information Act (FOIA) exemption that applies to most information in system of records is b. 6, Invasion of personal privacy. FOIA exemptions outline the types of information that can be withheld from public disclosure, and exemption 6 protects personal privacy rights. This includes records that contain personal information such as medical records, social security numbers, and other sensitive data.