Physics
Superconductors are substances which

conduct electricity at low temperature
offer no resistance to the flow of electricity
offer high resistance to the flow of current
conduct electricity at high temperatures

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Physics
The blue colour of sky is due to

Scattering of longer wavelengths of sunlight in the atmosphere
Refraction of sunlight
Reflection of sunlight
Scattering of shorter wavelengths of sunlight in the atmosphere

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Physics
Radiocarbon is produced in the atmosphere as a result of

Action of solar radiations particularly cosmic rays on carbon dioxide present in the atmosphere.
Lightning discharge in atmosphere.
Action of ultraviolet light from the sun on atmospheric oxygen.
Collision between fast neutrons and nitrogen nuclei present in the atmosphere.

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