Which gas is NOT considered IDLH (Immediately Dangerous to Life and Health)?

Nitrogen is considered safe in typical atmospheric concentrations, as it makes up about 78% of the Earth's atmosphere and is not toxic. It does not pose an immediate threat to life and health under normal conditions, thereby not being classified as an IDLH substance. IDLH gases are those that can pose immediate threats to life, cause irreversible health effects, or prevent escape in emergencies.

In contrast, hydrogen cyanide and carbon monoxide are both toxic gases that can cause severe health effects or death upon exposure, qualifying them for IDLH status. Argon, while inert and not toxic, can still displace oxygen in high concentrations, creating an asphyxiation hazard in confined spaces, warranting caution in certain situations. Thus, nitrogen stands out as the only gas in the list that does not present an IDLH scenario when present in the atmosphere.