Which type of icing is associated with the smallest size of water droplet?

Rime ice is characterized by the formation of ice that occurs when supercooled water droplets come into contact with a cold surface and freeze rapidly. The droplets that contribute to rime ice are typically small; they usually have a diameter of less than 25 microns. This is significant because the smaller the water droplet, the more likely it is to freeze quickly upon impact, creating the lightweight, granular structure associated with rime ice.

In contrast, clear ice forms from larger droplets that freeze slowly, leading to a smooth and transparent finish as they accumulate. Frost ice, which is a type of frost, develops primarily under conditions where the temperature of a surface is low enough for moisture in the air to crystallize directly upon contact, rather than from water droplets. Mixed ice incorporates elements from both clear and rime ice, often involving larger droplets alongside smaller ones. Therefore, these types of ice are associated with larger droplet sizes compared to rime ice.

The key distinction of rime ice involves both the size and behavior of the droplets involved in its formation, making it the correct answer for this question.