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What is the relationship between the relative molecular mass of a gas and its vapour density?
AMolecular mass = vapour density / 2
BMolecular mass = 2 x vapour density
CMolecular mass = vapour density
DMolecular mass = 4 x vapour density
Answer & Solution
Correct answer: B. Molecular mass = 2 x vapour density
1. Vapour density compares a gas to hydrogen, which is diatomic.
2. This gives $\text{V.D.} = \dfrac{\text{relative molecular mass}}{2}$.
3. Cross-multiplying gives relative molecular mass $= 2 \times$ vapour density.
Option A inverts the correct relationship.
_Source: Samacheer Kalvi (TN SCERT) Class 10 Science, Unit 7 Atoms and Molecules "Vapour Density and Relative Molecular Mass", p.106_
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