At high altitudes , water boils at a lower temperature because

Options

A. the atmospheric pressure is high at high altitudes
B. the viscosity of water is reduced at altitudes
C. the atmospheric pressure is low at high altitudes
D. the surface tension of water is reduced at high altitudes .

Explanation

To understand why water boils at a lower temperature at high altitudes, we can break down the explanation into a series of logical steps:

### Step-by-Step Solution:

1. **Understanding Boiling Point**: The boiling point of a liquid is the temperature at which its vapor pressure equals the surrounding atmospheric pressure. For water at sea level, this temperature is 100°C.

2. **Vapor Pressure**: Vapor pressure is the pressure exerted by the vapor in equilibrium with its liquid at a given temperature. As the temperature of the liquid increases, its vapor pressure also increases.

3. **Role of Atmospheric Pressure**: At sea level, the atmospheric pressure is approximately 101.3 kPa. For water to boil, its vapor pressure must reach this atmospheric pressure.

4. **Effect of Altitude on Atmospheric Pressure**: At higher altitudes, the atmospheric pressure decreases. For example, at a high altitude, the atmospheric pressure might be around 80 kPa or even lower.

5. **Lower Resistance to Vapor Pressure**: Since the atmospheric pressure is lower at high altitudes, the vapor pressure of water does not need to reach as high a value to equal the surrounding pressure. This means that water can boil at a lower temperature.

6. **Conclusion**: Therefore, at high altitudes, because the atmospheric pressure is lower, water boils at a temperature lower than 100°C. This explains why cooking or boiling water takes longer at high altitudes.

### Final Answer:
At high altitudes, water boils at a lower temperature because the atmospheric pressure is lower, which means the vapor pressure of water reaches the surrounding pressure more easily, allowing it to boil at a lower temperature.

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