The main reason why vegetables take longer to cook in boiling water at high altitudes is because:

Water boils at a higher temperature with higher altitude
The temperature of the boiling water decreases with increasing altitude
There is less oxygen in the air at high altitude
Saturation vapor pressure decreases with increasing altitude

The correct answer is: D. Saturation vapor pressure decreases with increasing altitude.

The boiling point of water is the temperature at which the vapor pressure of the liquid equals the external pressure surrounding the liquid. At sea level, the boiling point of water is 212 degrees Fahrenheit (100 degrees Celsius). However, as the altitude increases, the atmospheric pressure decreases. This causes the vapor pressure of the water to decrease, and the boiling point of water to decrease as well.

When vegetables are cooked in boiling water, the heat from the water causes the water molecules to move faster and faster. Eventually, the water molecules have enough energy to escape from the surface of the water and enter the air as water vapor. This process is called evaporation.

The rate of evaporation depends on the temperature of the water and the vapor pressure of the water. At higher altitudes, the boiling point of water is lower, and the vapor pressure of the water is also lower. This means that water molecules evaporate more slowly at higher altitudes.

As a result, it takes longer for vegetables to cook in boiling water at high altitudes. This is because the water molecules are not evaporating as quickly, and the heat from the water is not being transferred to the vegetables as efficiently.

Here is a brief explanation of each option:

  • Option A: Water boils at a higher temperature with higher altitude. This is not true. The boiling point of water decreases with increasing altitude.
  • Option B: The temperature of the boiling water decreases with increasing altitude. This is true. The boiling point of water decreases with increasing altitude.
  • Option C: There is less oxygen in the air at high altitude. This is true. The atmospheric pressure decreases with increasing altitude, and this causes the amount of oxygen in the air to decrease.
  • Option D: Saturation vapor pressure decreases with increasing altitude. This is true. The saturation vapor pressure is the pressure at which the water vapor in the air is in equilibrium with the liquid water. The saturation vapor pressure decreases with increasing altitude.
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