Which agent acts on a chemical reaction and absorbs heat for Class B and C fires?

The dry chemical extinguishing agent is effective for Class B and C fires because it not only suppresses flames but also interrupts the chemical reaction that fuels combustion. Such agents work by absorbing heat, which is essential for extinguishing a fire.

In Class B fires, which involve flammable liquids, the dry chemical can coat the surface of the liquid, preventing vapors from igniting. For Class C fires, which involve electrical components, these agents are non-conductive, making them safe to use on live electrical equipment. The ability of dry chemical agents to cut off the chemical supply to the fire and absorb heat makes them versatile and efficient in a variety of fire scenarios.

Other options, while they may be used for different fire classes or circumstances, do not provide the same combination of properties that dry chemical extinguishing agents do for Classes B and C.