How much did poison gas weigh?

The weight of poison gas can vary significantly depending on its chemical composition. For example, chlorine gas has a molecular weight of about 35.5 g/mol, while phosgene has a molecular weight of approximately 98 g/mol. Generally, gases are measured in terms of their density relative to air, which has an average molecular weight of about 29 g/mol, rather than a specific weight. Thus, the weight of poison gas is context-dependent and varies with the specific type of gas in question.