Which conditions result in the formation of frost?

The formation of frost occurs under specific atmospheric conditions that involve temperature and humidity. When the temperature of a collecting surface drops to or below the dewpoint of the adjacent air, and that dewpoint is below freezing, frost can form. This happens because the moisture in the air condenses onto the surface as ice rather than as liquid water.

In this scenario, the temperature must be at or below the dewpoint to ensure that the air's capacity to hold moisture is less than that which exists, leading to deposition of water vapor as solid frost on cold surfaces. The requirement that the dewpoint must also be below freezing ensures that the ice crystals form instead of liquid water.

The other conditions mentioned do not lead to frost formation. For example, if the temperature of the collecting surface is at or above the dewpoint, no condensation occurs, and therefore no frost can form. High humidity with elevated temperatures also does not favor frost; in fact, warm conditions typically promote moisture in the air without leading to freezing, thereby inhibiting frost formation. Wind speeds above 10 knots may influence frost by dispersing cold air, but they do not directly cause or inhibit frost formation in the same way that the listed correct answer conditions do.