Which of the following is the most effective way to prevent beer skunking?

Using dark bottles is the most effective way to prevent beer skunking because skunking is primarily caused by exposure to light, particularly ultraviolet (UV) light. When beer is exposed to UV light, a chemical reaction occurs that leads to the formation of off-flavors commonly associated with the skunky aroma. Dark bottles, which can be brown or green, are designed to block out a significant portion of this harmful UV light, thereby preserving the beer's intended flavor and aroma.

While other methods, such as storing beer in a cool place, can help maintain overall quality and freshness, they do not specifically target the risk of skunking due to light exposure. Airing the beer before serving does not prevent skunking; in fact, it could lead to oxidation if the beer is left open for too long. Adding preservatives might help with shelf stability, but they do not directly address the issue of light exposure that causes skunking.