Final answer:
Water vapor in the air has a longer mean free path than liquid water because its molecules are more spread out, leading to fewer collisions, whereas the molecules in liquid water are closer together, causing more frequent collisions and a shorter mean free path.
Step-by-step explanation:
The original question about the air content being indicated by the final meter reading when using less than 2.5 pints of alcohol is likely an error or irrelevant to the discussion on the mean free path of molecules in liquid water and water vapor.
Regarding mean free path, water vapor in the air has a longer mean free path compared to liquid water. The mean free path refers to the average distance a molecule travels before colliding with another molecule. Since liquid water has molecules that are much closer together, the frequency of collisions is higher, leading to a shorter mean free path. In contrast, water vapor, being in the gaseous state, has molecules that are more spread out, resulting in fewer collisions and therefore a longer mean free path.