Final answer:
Contrails are an example of a mixing cloud formed when hot exhaust gases from jet engines mix with cold air in the atmosphere, causing water vapor to condense into ice crystals.
Step-by-step explanation:
A contrail is an example of a mixing cloud. Contrails are formed when the hot exhaust gases from jet engines mix with the cold air in the atmosphere. This mixing causes the water vapor in the exhaust gases to condense into tiny ice crystals, forming a cloud-like trail behind the aircraft.