What is typically a characteristic of dry chemical extinguishing agents?

Dry chemical extinguishing agents are known for their ability to suppress fires while leaving behind a residue. This residue can often be a result of the chemical composition used in these agents, such as ammonium phosphate or sodium bicarbonate, which are common in multi-purpose dry chemical extinguishers. The residue left by these agents can sometimes pose a clean-up challenge after a fire incident, as it can coat surfaces and may require special cleaning.

By contrast, the other options do not reflect typical characteristics of dry chemical agents. For instance, they do not conduct electricity, making them safe for use on electrical fires. Additionally, they do not absorb moisture, and while they can be effective on Class B fires (flammable liquids), they are also effective on several other classes of fires, such as Class A (ordinary combustibles) and Class C (electrical fires). Therefore, the defining feature of leaving a residue is what distinguishes them as dry chemical extinguishing agents.