At what oxygen level might a person begin to feel disoriented?

A person might begin to feel disoriented at an oxygen level of 19.5%. This concentration is significant because it is notably below the normal atmospheric oxygen level, which is approximately 20.8%. At levels around 19.5%, the body starts to experience mild hypoxia, leading to symptoms such as dizziness, confusion, and impaired judgment. This drop in oxygen can affect cognitive functions and overall awareness, making it difficult for a person to think clearly or respond appropriately to their environment.

Lower oxygen levels, such as 18% and 16%, further exacerbate these symptoms, leading to more severe cognitive impairment and physical effects. Therefore, while reduced oxygen levels continue to affect individuals as they decrease, the threshold for noticeable disorientation begins at the 19.5% mark, making this the correct answer.