If temperature falls but air humidity greatly increases in a region, what is the correct analysis of the pressure effect?
Correct answer: B
At a comparable level, cooling makes air denser and therefore tends to increase its weight and pressure. Greater humidity means that more water-vapour molecules replace heavier nitrogen and oxygen molecules, making the moist air less dense and tending to reduce pressure. The net result depends on the relative strength of both effects, so option B is the valid analysis.