Density of Humid Air – Rankers Physics

Kinetic Theory of Gases: Practice Problem & Solution

Assertion (A): Density of humid air is less then density of dry air at the same temperature and pressure. Reason (R): Mass of humid air is more than mass of dry air.  
Both (A) & (R) are true and the (R) is the correct explanation of the (A)
Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
(A) is true but (R) is false
Both (A) and (R) are false

Solution Explained:

To solve this problem, we apply the core principles of Kinetic Theory of Gases. Understanding the underlying formula is key to arriving at the correct answer below:

Water vapor \( H_2 O \) has a lower molar mass (approx. \(18 g/mol\) than nitrogen \( 28 g/mol\) and oxygen (\32 g/mol). Thus, replacing dry air molecules with \( H_2 O\) makes humid air less dense. Reason (R) is incorrect.

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