The name given to a liquid drop of dew that freezes when the air temperature drops below freezing is:

The correct answer is: D. White frost.

White frost is a thin layer of ice crystals that forms on objects when the air temperature drops below freezing. It is most common on clear nights when the ground is cold and there is little wind. The ice crystals form when water vapor in the air condenses on objects and then freezes.

Frost can be a nuisance, as it can make surfaces slippery and difficult to walk on. However, it can also be beautiful, as it can create a delicate and ethereal appearance on objects.

The other options are incorrect because:

• Frost is a general term for ice crystals that form on objects when the air temperature drops below freezing. It can be white, black, or gray.
• Black frost is a type of frost that forms on objects when the air temperature is below freezing and there is little wind. It is caused by the sublimation of water vapor from the ground.
• Hoarfrost is a type of frost that forms on objects when the air temperature is below freezing and there is a lot of wind. It is caused by the condensation of water vapor in the air onto objects.
• Frozen dew is a type of frost that forms when dew freezes on objects. It is most common on clear nights when the air temperature drops below freezing.