Which of the discussed biogeochemical cycle(s)contribute(s) to formations of dead zones (areas with oxygen of 2mg/L or less) and formation of photochemical, toxic ozone? The C cycle The N cycle The N and the H cycle. ) The H cycle

The formation of dead zones (areas with oxygen levels of 2 mg/L or less) and the formation of photochemical, toxic ozone are primarily influenced by the nitrogen cycle (N cycle).<br /><br />1. **Dead Zones**: Dead zones are often caused by nutrient pollution, particularly from nitrogen and phosphorus. Excessive nitrogen from agricultural runoff, sewage, and industrial discharges can lead to eutrophication in water bodies. This process results in algal blooms, which, when they die and decompose, consume large amounts of oxygen, leading to hypoxic conditions (low oxygen levels).<br /><br />2. **Photochemical, Toxic Ozone**: The formation of ground-level ozone (a key component of smog) is a result of photochemical reactions involving nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the presence of sunlight. Nitrogen oxides are primarily emitted from combustion processes, such as those in vehicles and industrial activities.<br /><br />Therefore, the correct answer is:<br /><br />**The N cycle**