Concept:Vapor pressure is inversely related to the strength of intermolecular forces. Weaker forces mean less energy is required for molecules to escape into the vapor phase, resulting in high volatility (high vapor pressure).
Formula:$$ \text{V.P.} \propto \frac{1}{\text{IMF Strength}} $$
Solution:- Water (\( \text{H}_2\text{O} \)), Hydrogen fluoride (\( \text{HF} \)), and Acetic acid (\( \text{CH}_3\text{COOH} \)) all contain highly electronegative atoms covalently bonded to hydrogen. Consequently, they all exhibit massive, highly stabilizing hydrogen bonding networks.
- Petrol (a mixture of hydrocarbons like octane) is entirely non-polar. It cannot form hydrogen bonds or dipole-dipole attractions.
- Because Petrol is held together solely by weak London dispersion forces, its molecules easily and rapidly escape into the air. Thus, it exerts a massively higher vapor pressure compared to the others.
Why other options are incorrect:The robust hydrogen bonding in water, HF, and acetic acid anchors their molecules in the liquid state, severely dampening their vapor pressures.
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