Which audiogram symbol represents air conduction unmasked?

The symbols that represent air conduction unmasked on an audiogram are the "X" and "O." The "X" is typically used to indicate the results of air conduction testing for the left ear, while the "O" represents the right ear. This notation is used in audiometry to visually differentiate between the ears when assessing hearing sensitivity.

The choice of "X" and "O" is standard practice in audiological assessments, making it easy for practitioners to interpret and compare hearing thresholds for both ears. Recognizing these symbols is fundamental for accurate representation of test results and clear communication of hearing health status.

Other symbol combinations provided in the question do not represent unmasked air conduction. Each of those symbols corresponds to different types of hearing tests or special conditions, but they do not fulfill the standard convention for unmasked air conduction representation.