Physics
Choose the most appropriate answer: Natural radioactivity was discovered by

Henry Bacquerel
Earnest Rutherford
Marie Curie
Enrico Fermi

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Physics
What is refractive index ?

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 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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