Which mixture will weigh the least?

To determine which mixture weighs the least, it is essential to consider the density and molecular weight of the components involved. Dry air has a typical molecular weight of about 29 g/mol, while water vapor has a molecular weight of about 18 g/mol.

In the scenario where there are 35 parts of dry air mixed with 65 parts of water vapor, the resulting mixture will have a lower overall weight per given volume compared to the other options. This is because a greater proportion of the lighter water vapor (which weighs less than dry air) is included in the mixture, effectively reducing the average weight of the mixture.

In comparison, the mixtures containing higher proportions of dry air will result in a heavier overall weight because dry air has a higher molecular weight. The combinations that have larger ratios of dry air (like 100 parts dry air, 50 parts dry air and 50 parts water vapor, and 70 parts dry air and 30 parts water vapor) will thus weigh more than the mixture of 35 parts dry air and 65 parts water vapor.

The balance of lighter water vapor against heavier dry air plays a crucial role in determining the overall weight of the mixture, making the mixture of 35 parts dry air and 65 parts water