Odor threshold is defined as the concentration above which an individual can detect a vapor or gas using their sense of smell.

• A. The concentration at which a substance changes color.
• B. The concentration above which an individual can detect a vapor or gas using their sense of smell.
• C. The level of odor required for a sensor to function.
• D. The threshold for odorless substances.

Answer: (B)

Odor threshold is about human perception: it’s the minimum concentration at which a person can detect an odor with their sense of smell. The statement that defines it as the concentration above which a vapor or gas can be detected by smell matches the standard meaning, focusing on how people perceive odors rather than on visual cues or instrument sensors. In practice, these thresholds are compound-specific and can vary between individuals and environmental conditions, and they’re usually reported in units like ppm or mg/m3 for gases. The other options describe color changes, sensor-based detection, or odorless substances, none of which capture the idea of detecting an odor by the human nose.