Detailed Explanation:

Answer: Option 2 — Clouds reflect back the Earth's radiation.

Dewdrops form when the Earth's surface cools below the dew point through radiation heat loss on clear nights. On cloudy nights, clouds act as a blanket by reflecting the Earth's longwave radiation back to the surface, preventing sufficient cooling. This keeps the temperature above the dew point, thus preventing dew formation.

📝 Short Notes: Dew Formation and Radiation

• Dew Formation: Dew forms when water vapor in the air condenses on cool surfaces when the surface temperature drops to or below the dew point.
• Radiational Cooling: On clear nights, the Earth's surface radiates heat (longwave infrared radiation) into space, causing surface temperatures to drop rapidly.
• Role of Clouds: Clouds contain water droplets that absorb and reflect back the Earth's outgoing longwave radiation, acting as an insulating blanket.
• Greenhouse Effect: This reflection by clouds is similar to the greenhouse effect, where certain atmospheric components trap heat near the surface.
• Clear vs Cloudy Nights: Clear nights experience maximum cooling and dew formation, while cloudy nights remain warmer with minimal or no dew.
• Dew Point: The temperature at which air becomes saturated (100% relative humidity) and water vapor begins to condense.