Which of the following is classified as an explosive gas?

Hydrogen is classified as an explosive gas due to its high flammability and the specific conditions under which it can react with oxygen. When hydrogen gas is mixed with air or oxygen in certain concentrations, it can ignite and cause a rapid release of energy, resulting in an explosion. This characteristic is particularly significant in applications related to wastewater treatment and gas handling, where caution must be exercised to prevent dangerous situations.

In contrast, the other gases listed—carbon dioxide, argon, and nitrogen—do not possess the same explosive properties. Carbon dioxide is generally non-flammable and is used in fire suppression systems. Argon is an inert gas and does not react in explosive situations, while nitrogen is also non-reactive under normal conditions and is often used to create an inert atmosphere, which prevents fires and explosions. Understanding the properties of these gases is crucial in ensuring safety in environments where they may be present.