At the same conditions of pressure and temperature ammonia gas is less dense than air why is this true

According to Marriotte's law, we can use a formula that's a derivation of the original law. That formula says that pressure multiplied by the molar mass, and then divided by R (a constant value) multiplied by the temperature, equal the specific mass of a gas, for example. If we are considering the same temperature and pressure for the air and the ammonia gas then the only difference is really on the molar mass of the gas. The molar mas for air is 0.029 kg/mole and the molar mass for the ammonia gas is 0.017 kg/mol. Just from here we see that the ammonia gas will be less dense then the air.