Final answer:
Hail is formed when water droplets in a thundercloud freeze into lumps of ice.
Step-by-step explanation:
When water droplets in a thundercloud freeze into lumps of ice, it forms hail. Hail is formed when the water droplets in a thundercloud are carried upward by strong updrafts and freeze as they encounter below freezing temperatures. The frozen droplets then continue to grow as they are carried up and down within the cloud, accumulating layers of ice until they become too heavy and fall as hailstones.