MCQ Detailed View

The boiling point of pure water is 100 °C (212 °F) when measured at standard atmospheric pressure (1 atmosphere or 101.3 kPa). The boiling point is defined as the temperature at which the vapor pressure of a liquid becomes equal to the surrounding external pressure, allowing the liquid to change into vapor throughout its bulk.

At temperatures below the boiling point, evaporation can occur, but only from the surface of the liquid. At the boiling point, however, bubbles of vapor form inside the liquid and rise to the surface, leading to rapid vaporization.

It is important to note that the boiling point of water is not always constant. While 100 °C is correct at sea level (1 atm pressure), the boiling point changes with variations in external pressure:

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  At higher altitudes, atmospheric pressure is lower, so water boils at a temperature lower than 100 °C. For example, at the top of a mountain, water may boil at 90 °C or even less.

  
  


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  At pressures higher than 1 atm, such as in a pressure cooker, the boiling point of water increases above 100 °C. This is why food cooks faster in a pressure cooker.

  
  

The boiling point of water is a fundamental reference point in physics and chemistry. It was historically used to help define the Celsius temperature scale, where 0 °C represents the freezing point of water and 100 °C represents its boiling point under normal conditions.

Understanding the boiling point is important in thermodynamics, everyday science, cooking, and industrial applications. It explains why water turns into steam, how steam engines work, and why different environments affect boiling and cooking.

Thus, the correct answer is 100 °C, which is the boiling point of pure water at standard atmospheric pressure.