Which process is critical for maintaining the balance of oxygen and carbon dioxide in the atmosphere?

Photosynthesis is essential for maintaining the balance of oxygen and carbon dioxide in the atmosphere because it is the process by which plants, algae, and certain bacteria convert carbon dioxide and water into glucose and oxygen, using sunlight as energy. During this process, organisms absorb carbon dioxide, which is a greenhouse gas and a primary contributor to global warming, and release oxygen as a byproduct. This not only helps to reduce the levels of carbon dioxide in the atmosphere but also supports life on Earth by providing oxygen for respiration.

The other processes listed do not play a significant role in the balance of these gases. Evaporation and condensation are part of the water cycle and primarily involve the transition of water between states (liquid to vapor and vapor to liquid, respectively) but do not directly affect atmospheric gases. Combustion, while it does produce energy, results in the release of carbon dioxide alongside water vapor, thus contributing to greenhouse gas emissions rather than helping to balance them. Therefore, photosynthesis is the key process that sustains atmospheric equilibrium between oxygen and carbon dioxide.