Here's why:

* Chlorine's Molecular Weight: Chlorine (Cl₂) has a molecular weight of approximately 71 g/mol.

* Air's Average Molecular Weight: Air is a mixture of gases, primarily nitrogen (N₂) and oxygen (O₂). Its average molecular weight is about 29 g/mol.

Since chlorine has a significantly higher molecular weight than air, it is denser. This means a volume of chlorine gas will weigh more than the same volume of air.

Important Note: Chlorine is a toxic gas and should only be handled by trained professionals in a controlled environment.