The most effective practice in protecting personally identifiable information (PII) from unauthorized access in a cloud environment is to utilize encryption with logical access controls. Encryption is a technique that transforms the data into an unreadable or unintelligible form, making it inaccessible or unusable by unauthorized parties. Logical access controls are the mechanisms or rules that regulate who can access, view, modify, or delete the data, based on their identity, role, or privilege. By utilizing encryption with logical access controls, the PII can be protected from unauthorized access, disclosure, or theft, both in transit and at rest, in a cloud environment. The other options are not as effective as utilizing encryption with logical access controls, as they are related to the classification, separation, or audit of the data, not the protection or security of the data. References = Risk and Information Systems Control Study Manual, Chapter 3: IT Risk Response, Section 3.3: IT Risk Response Implementation, page 145.