Final answer:
Fog formation requires water vapor to condense when the air reaches its dew point, after which the relative humidity becomes 100%. A temperature drop that results in saturation will trigger this condensation process. Calculating the specific grams of water that must condense from a cubic meter of air involves knowing the saturation vapor content at two different temperatures.
Step-by-step explanation:
To determine the amount of water that must condense out of the air for fog to form, we should consider the concept of relative humidity and the temperature-dependent maximum water vapor the air can hold. The temperature drop from 25.0°C to 15.0°C means that the air can hold less water vapor at 15.0°C. If the relative humidity is initially 90% at 25.0°C, a temperature drop to 15.0°C could result in saturation (100% relative humidity). This excess water vapor would then condense into water droplets, forming dew or fog if the droplets are small enough to remain suspended in the air.
To calculate the specific amount of water that must condense, we can use saturation vapor pressure tables or equations to find the maximum amount of water vapor the air can hold at 25.0°C and 15.0°C. The difference in these amounts, adjusted for the initial relative humidity, gives us the amount of water that needs to condense out. This value represents the grams of water per cubic meter of air that would turn into condensation.