from which type of clouds do hail pellets form?\n○ cirrus\n○ cumulonimbus\n○ nimbostratus\n○ stratus

Brief Explanations:

Hail pellets form in cumulonimbus clouds. These are large, vertical clouds associated with thunderstorms. Strong updrafts within cumulonimbus clouds carry water - droplets high into the atmosphere where they freeze and accumulate to form hailstones. Cirrus clouds are high - altitude, thin and wispy clouds not associated with hail formation. Nimbostratus clouds are associated with continuous rain, not hail. Stratus clouds are low - lying, uniform clouds that usually bring light precipitation like drizzle, not hail.

Answer:

cumulonimbus