Description:

The correct answer is:

✅ Condensation of water droplets

Why?

Fog forms when water vapor condenses into tiny droplets near the ground, reducing visibility. Key causes:

Radiative Cooling: Clear nights allow ground heat to escape, cooling air to its dew point (→ radiation fog).

Advection: Warm, moist air moves over cold surfaces (e.g., coastal sea fog).

Upslope Fog: Air cools as it rises over hills.

Impact on Visibility:

Dense fog can lower visibility to <1 km (0.6 mi), disrupting:

Driving (risk of pileups).

Flights (delays/cancellations).

Why Not the Others?

❌ Air pollution: Can worsen haze but doesn’t cause fog.

❌ Wind direction: May transport fog but isn’t its root cause.

Fun Fact: London’s historic "pea soup fog" mixed coal smoke + fog—now rare due to clean-air laws! 🌫️🇬🇧

Safety Tip: Use low-beam headlights in fog—high beams reflect back! 🚗💡