Which of the following gases is primarily responsible for buoyancy effects underwater?

Nitrogen is primarily responsible for buoyancy effects underwater due to its prevalence in the air we breathe and its solubility in water. When a diver descends, the pressure increases, causing the gases within the body and any bubbles to compress, impacting buoyancy. Nitrogen, being a major component of the air at 78%, influences the overall density of a diver's body and equipment when submerged.

While other gases like oxygen and helium are present, their contributions to buoyancy are less significant in comparison to nitrogen. Carbon dioxide, although it plays a role in respiration, is not a primary factor in buoyancy. Nitrogen's properties, along with its solubility and interaction with other gases under pressure, make it the key element affecting buoyancy during a dive. Thus, understanding nitrogen's role is essential for divers to manage their buoyancy properly.