Which of the following is a sensory indicator of chemical reactions?

• A. Colored vapor clouds
• B. Peculiar smells
• C. Heat
• D. Unusual temp drop

Answer: (A)

Seeing colored vapor clouds is a clear, immediate sign that a chemical reaction is producing airborne material. It’s a visual cue you can observe from a safe distance, which is crucial in hazmat scenarios because it signals a potential release of hazardous substances. While smells can indicate a reaction, they’re not reliable—some gases are odorless, and odors can be masked or harmful to inhale. Heat or a temperature change can occur with reactions but aren’t always present or easy to detect without instruments. The visual cue of colored vapor clouds stands out as a dependable, identifiable indicator, making it the best single sensory sign among the options.