The specific gravity of a gas is a ratio of its density to the density of what?

The specific gravity of a gas is defined as the ratio of the density of that gas to the density of air at standard conditions. This metric is significant because it provides insight into how the gas will behave in relation to air. When the specific gravity is less than one, the gas will rise in air; when it is greater than one, it will tend to sink.

Understanding specific gravity is crucial in various applications, including safety assessments and operational guidelines in industries that involve gas. It helps in determining the proper ventilation requirements, leak detection strategies, and overall safety measures when working with different gases.

The other options, such as water, carbon dioxide, and oxygen, do not provide a relevant point of reference for comparing the majority of gases we encounter under standard conditions. Air serves as the common reference because it is the medium most gases will interact with in many situations.