Final answer:
At a temperature of -5°C in the lower part of an altostratus cloud, you would encounter rime ice, characterized by its rough, milky-white appearance as it forms from the rapid freezing of supercooled droplets.
Step-by-step explanation:
If you are climbing through the lower part of an altostratus cloud at a temperature of -5°C, you could expect to encounter rime ice. Rime ice forms when supercooled water droplets freeze onto objects upon contact, which could be an aircraft or other objects passing through the cloud. These conditions are typical when the temperatures are between 0°C and -20°C. Unlike clear ice, which forms from large droplets that spread before freezing, rime ice forms quickly as the small supercooled droplets freeze almost instantly, resulting in a rough, milky-white ice.