1. Understand Density

* Density is mass per unit volume. The denser a substance is, the more mass it has in a given volume.

* We need to compare the densities of ammonia (NH₃) and hydrogen chloride (HCl) gas.

2. Molecular Weights

* Ammonia (NH₃): 14.01 g/mol (nitrogen) + 3 * 1.01 g/mol (hydrogen) = 17.04 g/mol

* Hydrogen Chloride (HCl): 1.01 g/mol (hydrogen) + 35.45 g/mol (chlorine) = 36.46 g/mol

3. Ideal Gas Law (Approximation)

* The ideal gas law tells us that equal volumes of gases at the same temperature and pressure contain the same number of molecules.

* Since HCl has a higher molecular weight than NH₃, a given volume of HCl gas will contain more mass than the same volume of ammonia gas.

Conclusion:

1 dm³ of hydrogen chloride gas (HCl) weighs more than 1 dm³ of ammonia gas (NH₃).