Question

The weight of humid air is ____ to then dry air.
A. more
B. less
C. equal
D. equivalent

Answer 1

Hint: Dry air is mostly made up of nitrogen and oxygen molecules, to make a given volume of air moist we need to add water vapor molecules to the volume. In order, to make a given volume of air moist water molecules are added, the heavier molecules are replaced by lighter molecules.

Complete answer: The atomic weight of a water molecule (H2O) is 18, free nitrogen (N2) is 28 and an oxygen molecule (O2) has an atomic weight of 32. This concludes that the water molecule is lighter than an oxygen or nitrogen molecule. If both the humid air and dry air are at the same temperature and pressure then they will have the same number of molecules. Dry air is mostly made up of nitrogen and oxygen molecules, to make a given volume of air moist we need to add water vapor molecules to the volume. In order, to make a given volume of air moist water molecules are added, the heavier molecules are replaced by lighter molecules. Therefore, as water molecules are lighter than oxygen and nitrogen molecules, humid air is lighter than dry air.
- Option A: Humid air can’t weigh more than dry air. Hence, this is an incorrect option.
- Option B: Humid air weighs less than dry air. Hence, this is the correct option.
- Option C: Humid air and dry air can’t weigh equal. Hence, this is an incorrect option.
- Option D: The weight of humid air is not equivalent to that of dry air. Hence, this is an incorrect option.



Note: The atomic weight is used to represent the individual weight of an atom. The atomic weight of Hydrogen(H) is 1, Carbon (C) is 12, Nitrogen (N) is 14, and Oxygen (O) is 16.