The correct option is Nimbostratus.
Explanation
Clouds are classified based on their altitude, stretch, density, and transparency. They are generally categorized into four groups: High clouds (8-12 km), Middle clouds (2-6 km), Low clouds (ground to 2 km), and Clouds with extensive vertical development.Analysis of Options:
- Altostratus Altostratus (Incorrect): The prefix "Alto" indicates middle clouds. These form at altitudes between 2 km and 6 km and typically appear as watery, fibrous sheets.
- Cirrostratus Cirrostratus (Incorrect): The prefix "Cirro" indicates high clouds. These form at altitudes between 8 km and 12 km and are known for creating halos around the sun or moon.
- Nimbostratus Nimbostratus (Correct): These are classified as Low clouds (forming below 2 km). They appear as dense, shapeless, and dark grey layers that block sunlight and are associated with continuous precipitation.
- Cumulonimbus Cumulonimbus (Incorrect): While their base is often low, these are distinctively classified as clouds with extensive vertical development. They extend vertically through the atmosphere and are associated with thunderstorms and heavy rain.
Key Takeaway:
Nimbostratus is a low-level rain cloud. The prefixes "Cirro-" and "Alto-" denote high and middle clouds respectively, while Cumulonimbus is a vertical thundercloud.