What is the appropriate way to express uncertainty to a superior?

The appropriateness of expressing uncertainty to a superior is best reflected in the first choice. By stating "I'm not sure, Sir/Ma'am," you communicate a clear acknowledgment of your uncertainty while maintaining the necessary respect and formality expected in a military or structured hierarchy. This phrase directly conveys your lack of information without appearing evasive or overly casual.

The other options, while attempting to convey uncertainty, lack the directness and respect that is crucial in communicating with a superior. Phrases like "Maybe," "It's possible," and "That could be" can come off as vague or indecisive, which may not be suitable when clarity and professionalism are needed in such interactions. Being straightforward while maintaining proper etiquette is key, making "I'm not sure" the most appropriate choice in this context.