MCQ Detailed View

The freezing point of water is defined as the temperature at which pure liquid water changes into a solid state (ice) under standard atmospheric pressure (1 atmosphere or 101.3 kPa). This temperature is 0°C (32°F). At this point, water molecules lose enough thermal energy to slow down and arrange themselves into a rigid, crystalline structure, forming ice.

The freezing process occurs because temperature is a measure of the average kinetic energy of molecules. As water cools, the motion of its molecules decreases. At 0°C, hydrogen bonds between water molecules become strong enough to lock them into a solid lattice structure, turning water into ice.

Factors that can alter the freezing point:

1. 
   

   Impurities or dissolved substances: Adding salts, sugar, or other solutes to water lowers its freezing point. This phenomenon is called freezing point depression, which is why seawater freezes below 0°C and why salt is spread on icy roads.

   
   


2. 
   

   Pressure variations: While pressure has a small effect on water's freezing point, under normal atmospheric conditions, it remains very close to 0°C.

   
   

The incorrect options:

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  -2°C and -4°C: These temperatures occur for water containing impurities or solutes but not for pure water under standard pressure.

  
  


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  None of above: Incorrect, as pure water has a well-defined freezing point of 0°C.

  
  

This physical property of water is a key reference point in temperature scales. The Celsius scale is based on the freezing point (0°C) and boiling point (100°C) of water under standard conditions.Thus, the correct answer is 0°C, the temperature at which pure water freezes and changes from liquid to solid under normal atmospheric conditions.