Which of the following fit-testing solutions is known for its bitter taste?

The correct choice, Bitrex, is known for its distinctly bitter taste, which makes it an effective solution for fit testing. Bitrex, scientifically known as denatonium benzoate, is one of the most bitter substances and is often used in various applications to prevent accidental ingestion of hazardous materials.

In the context of fit testing, the bitter taste of Bitrex enhances the reliability of the test by providing a clear and immediate sensory response if the respirator seal is not intact. When participants can taste Bitrex during the fit test, it indicates that air is leaking in, and the fit of the respirator may not be effective for protection.

Other options such as irritant smoke are used in fit testing as well but rely on irritant qualities rather than a taste response. Saccharin, although used in some fit-testing applications, is sweet in flavor, which does not provide the same immediate deterrent response as Bitrex. Isoamyl acetate has a strong banana-like scent, but again, it does not involve a taste mechanism like Bitrex does. Thus, Bitrex is uniquely known for its bitter taste, making it the appropriate choice for this question.