What percentage of the air is oxygen?

The correct answer is based on the composition of Earth's atmosphere, which consists of approximately 21% oxygen. This figure is widely accepted in scientific literature and is crucial for understanding various processes in agriculture, environmental science, and even human physiology. Oxygen is essential for respiration in both humans and animals, and it plays a significant role in the photosynthetic process of plants, where it is produced as a byproduct.

The other percentages listed do not reflect the actual composition of atmospheric air. Understanding this composition is foundational in agriculture, especially regarding plant growth and health, as well as in managing livestock and other agricultural practices.