Physics
The propagation of sound waves in a gas involves

Isochoric compression and rarefaction
Isobaric compression and rarefaction
Adiabatic compression and rarefaction
Isothermal compression and rarefaction

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Physics
What is refractive index ?

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

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