MCQ Detailed View

Snow on mountains does not melt immediately under sunlight because of a physical property called latent heat of fusion. The latent heat of fusion is the amount of heat energy required to change a substance from solid to liquid at its melting point without changing its temperature.

For water (and snow), the latent heat of fusion is 334 kJ/kg, which means a significant amount of energy is needed to convert 1 kilogram of ice or snow into water at 0°C. This energy is absorbed from the sunlight, but because the value is high, snow takes time to melt, even under strong sunlight.

Other factors mentioned in the options are incorrect:

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  It becomes very hard (Option 1) is not related to melting; hardness does not affect the heat required to melt snow.

  
  


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  It reflects most of the heat from the sun (Option 2) refers to albedo effect; while reflection reduces absorption slightly, the main reason for slow melting is latent heat.

  
  


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  Low specific heat capacity (Option 3) refers to how much temperature rises with heat; snow’s specific heat is moderate, but the slow melting is mainly due to latent heat.

  
  

When snow absorbs heat from sunlight, the energy first goes into breaking hydrogen bonds between water molecules, not into raising temperature. Only after absorbing enough latent heat does the snow start turning into liquid water. This is why mountain snow melts gradually, providing a sustained water supply to rivers and lakes, which is important for ecosystems and human use.Understanding latent heat of fusion helps students connect the concepts of thermodynamics, energy transfer, and phase changes in physics. It also explains natural phenomena such as snow melting patterns and glacial water flow.

In conclusion, snow on mountains melts slowly because it has a high latent heat of fusion (Option 4), requiring a large amount of energy to change from solid to liquid without increasing temperature.