What is the visibility range when fog is reported?

When fog is reported, visibility is defined as being reduced to less than 1 kilometer. Fog creates a dense suspension of water droplets in the air, which significantly limits how far a person can see. Specifically, according to aviation meteorological standards, fog is classified when visibility falls below this threshold of 1 kilometer. This classification helps pilots and air traffic control understand the potential hazards posed by reduced visibility conditions, impacting flight operations, takeoff, and landing decisions.

The other options represent broader visibility ranges that do not specifically align with the definition of fog, thus making those choices less accurate in this context.