CWEA Grade 4 Practice Test

Oxygen deficiency can occur due to gases that displace or dilute the available oxygen in the air. Carbon dioxide and nitrogen are particularly significant in this context. When carbon dioxide is present in high concentrations, it can displace oxygen because it takes up space in the atmosphere that is otherwise available for oxygen. Similarly, nitrogen, while a major component of Earth's atmosphere itself, does not support combustion and can dilute the oxygen concentration when present in large volumes or in enclosed spaces.

This makes the combination of carbon dioxide and nitrogen a realistic concern for environments where oxygen levels are crucial for health and safety, such as in industrial settings or confined spaces. The other combinations listed involve gases that either do not significantly affect oxygen levels in a harmful way or do not contribute directly to oxygen deficiency in the same manner as carbon dioxide and nitrogen.