Physics
An egg sinks in soft water but floats in a concentrated solution of salt because

Water has high surface tension
Albumin dissolves in salt solution and egg becomes lighter
The density of salt solution exceeds the density of eggs
Egg absorbs salt from the solution and expands

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Physics
Radiocarbon is produced in the atmosphere as a result of

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

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