At what humidity level can carburetor ice form?

Carburetor ice can form at humidity levels above 80%. This phenomenon occurs because as fuel vaporizes in the carburetor, it causes a drop in temperature due to the latent heat of vaporization. When the humidity is high, the air can hold more moisture, which can lead to the formation of ice in the carburetor. At humidity levels exceeding 80%, the air's capacity to retain moisture increases, making it more favorable for ice to develop under the right temperature conditions. Thus, the correct answer is associated with the specific moisture content in the air that heightens the risk of carburetor icing, especially when combined with lower temperatures.