* Molecular Weight: Chlorine gas (Cl₂) has a molecular weight of approximately 71 g/mol. Air, composed mostly of nitrogen (N₂) and oxygen (O₂), has an average molecular weight of about 29 g/mol. Since chlorine's molecular weight is significantly higher, it means a single chlorine molecule is heavier than an average air molecule.

* Density: Density is a measure of mass per unit volume. Because chlorine molecules are heavier, a given volume of chlorine gas will have a greater mass than the same volume of air. This higher density translates to chlorine gas being heavier than air.

Practical Implications:

The fact that chlorine gas is heavier than air has some important consequences:

* Leakage: If a chlorine gas leak occurs, the gas will tend to pool in low-lying areas, as it is heavier than air and will displace it. This makes it important to ensure good ventilation in areas where chlorine is stored or used.

* Safety: People should be aware of the potential for chlorine gas to accumulate in low-lying areas, especially in confined spaces. This is why chlorine gas leaks are particularly dangerous.