Which gases are measured by a multi-gas atmospheric monitor?

The correct choice encompasses a range of gases that are critical for safety monitoring in various environments, especially in confined spaces or areas where hazardous materials may be present. A multi-gas atmospheric monitor is designed to detect the levels of specific gases that pose health and safety risks.

Oxygen is essential because its deficiency can lead to asphyxiation. Carbon Monoxide is a dangerous byproduct of combustion, which can cause poisoning even at low concentrations. Hydrogen Sulfide is highly toxic and can be lethal, especially in high concentrations, and it is often found in industrial and wastewater settings. Hydrogen Cyanide is another highly toxic gas that can result from industrial processes or fires. Methane, while not toxic in itself, is flammable and poses a risk of explosion in certain concentrations.

The inclusion of these specific gases in option C reflects the typical focus of multi-gas monitors on both the detection of toxic gases and flammable substances, making it the most appropriate choice among the options presented.