The specific gravity standard for gases is?

The specific gravity standard for gases is based on air. Specific gravity is a dimensionless quantity that relates the density of a substance to the density of a reference substance. In the case of gases, air is typically used as the reference substance because it is abundant and readily available, which allows for easy comparisons across different gases.

When determining the specific gravity of a gas, it is calculated by taking the density of the gas and dividing it by the density of air under the same conditions of temperature and pressure. This standardization allows for a consistent way to evaluate the buoyancy of different gases in the atmosphere. Understanding specific gravity helps in applications such as ventilation, combustion, and various engineering processes, as it indicates whether a gas will rise or sink relative to air.

The other options, while they may represent valid gases, are not used as the standard reference for calculating the specific gravity of gases. Water vapor, oxygen, and nitrogen each have their own specific gravity, but they do not provide a universal baseline for comparison with other gases like air does. Air serves as the most practical and common standard in various calculations and industrial applications related to gas behavior.