Physics
The mercury and sodium street lamps light up because of :

Atomic emission
Electron absorption
Atomic absorption
Electron emission

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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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Physics
In a conductor

The forbidden energy gap is very wide
The valence band and the conduction band overlap each other
There is no conduction band
The forbidden energy gap is very narrow

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