Concept:A liquid boils when its internal vapor pressure becomes equal to the external ambient atmospheric pressure.
Formula:$$ P_{\text{vapor}} = P_{\text{atm}} \implies \text{Boiling occurs} $$
Solution:- As altitude increases (e.g., on a mountain), the column of air above is shorter and less dense, meaning the external atmospheric pressure is lower than standard \( 760 \text{ mmHg} \).
- Because the external pressure is reduced, the water does not need to be heated as much to raise its vapor pressure to match the surroundings.
- Consequently, water boils at a temperature lower than \( 100^\circ\text{C} \).
Why other options are incorrect:Atmospheric pressure is not higher at high altitudes. Hydrogen bonding is an intrinsic property of the water molecule and does not weaken simply due to altitude.
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