Which of the following gases is NOT commonly encountered on the job?

Oxygen is not commonly encountered in terms of environmental compliance inspections in the same way as the other gases listed. In routine environmental assessments, gases like carbon dioxide, methane, and chlorine are more frequently analyzed due to their relevance in air quality, emissions, and hazardous materials management.

Carbon dioxide is a significant greenhouse gas and often monitored in various industries for compliance with emissions standards. Methane, a potent greenhouse gas, is particularly relevant in inspections related to landfills, agriculture, and fossil fuel extraction, where it can be released into the atmosphere. Chlorine, on the other hand, is commonly used in water treatment and certain industrial applications, making it a focus in inspections for potential chemical exposure and compliance with safety standards.

Oxygen, while essential for life and often present in the environment, does not typically pose the same regulatory concerns or require monitoring in environmental inspections as the other gases mentioned. This is why it is considered the correct answer in this context.