Why can air density decrease with increasing humidity at the same temperature and altitude?
Answer and explanation
Correct answer: The molecular mass of water vapour is lower than that of the main gases in dry air
At the same temperature and pressure, water-vapour molecules have a molecular mass of about 18, whereas dry air is dominated by nitrogen and oxygen with an average molecular mass of about 29. Adding water vapour therefore replaces some heavier molecules with lighter ones. Consequently, humid air can be less dense than dry air under comparable conditions.
Frequently asked questions
What is the correct answer to this question?
The molecular mass of water vapour is lower than that of the main gases in dry air
Why is this the correct answer?
At the same temperature and pressure, water-vapour molecules have a molecular mass of about 18, whereas dry air is dominated by nitrogen and oxygen with an average molecular mass of about 29. Adding water vapour therefore replaces some heavier molecules with lighter ones. Consequently, humid air can be less dense than dry air under comparable conditions.
Which subject and chapter does this question cover?
This is a Class 12 Geography question. Chapter: Atmospheric Circulation and Weather Systems.
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