Physics
The snow on the mountains does not melt all at once when it is heated by the sun because:

It has a high latent heat of fusion
It reflects most of the heat from the sun
It becomes very hard
It has a low specific heat capacity

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Physics
What is refractive index ?

It is defined as the ratio of speed of light in vacuum to the speed of light in the medium.
None of above
It is defined as the ratio of speed of light in the medium to the speed of light in vacuum.
It is defined as the product of speed of light in medium and in vacuum.

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