Which of the following methods can be used to detect NH3?

Detecting ammonia (NH3) can effectively be accomplished using various sensory and physical methods. The correct choice of using soap and smell relies on the unique characteristics of ammonia as a gas. Ammonia has a distinct, pungent odor that can be detected by human senses at very low concentrations, making it easy to identify in the environment. When using soap or a soapy water solution, bubbles can form in the presence of ammonia gas, and this method is often used in leak detection scenarios because it allows for visual confirmation of gas presence through bubble formation.

Other methods listed may not be as direct or effective for detecting ammonia. For example, indicator strips and flame tests might not provide a reliable or precise measurement of ammonia concentrations. pH meters are more suitable for measuring acidity or alkalinity of solutions rather than directly detecting gas. Chromatography is a laboratory technique best suited for detailed analysis but is not practical for immediate field detection. Thermal cameras and gas masks are not direct detection methods; they are protective equipment or tools used in response to hazardous gases rather than for the detection of ammonia itself.