The dew point is defined as the temperature below which combustion products will what on exposed surfaces?

The dew point is the temperature at which air becomes saturated with moisture and can no longer hold all of the water vapor it contains. As the air cools to this point, the water vapor begins to condense into liquid droplets. This condensation occurs when the temperature drops to the dew point, leading to a formation of liquid water from the vapor phase.

In the context of combustion products, when the temperature of these products falls below the dew point, the moisture in the products will condense on exposed surfaces, potentially leading to corrosion or other issues in the system. This principle is crucial in HVAC and combustion applications, as managing the temperature and ensuring it stays above the dew point can prevent condensation and its associated problems.

The other options suggest processes that do not align with the nature of gas and vapor behavior in relation to temperature drops, specifically in the context of moisture. For instance, vaporizing refers to a state change from liquid to gas, igniting pertains to starting combustion, and evaporating signifies a transition from liquid to vapor at temperatures higher than the boiling point, which is not relevant to the dew point concept.