116. An extinguishing agent which effectively cools, dilutes combustible vapors and provides a heat and smoke screen is __________.

Water fog is the correct answer; it effectively cools fires, dilutes combustible vapors, and creates a heat and smoke screen due to its finely divided droplets which absorb heat, produce steam, and form a dense vapor cloud. Dry chemical, carbon dioxide, and Halon 1301 primarily function through chemical interruption or oxygen displacement, lacking the combined cooling, dilution, and screening properties of water fog.