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
When a piece of pure silicon is doped with aluminium, then

The doped silicon piece will become p-type
The doped silicon piece will become n-type
The resistivity of the doped silicon piece will increase
The conductivity of the doped silicon piece will remain the same

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Physics
Light houses are places with powerful lights to :

Guide and warn the ships coming from different directions in the ocean
Indicate to the incoming warships, the location of a harbour during night
Guide and help large crowds at religious gathering during nights
Guide and resolve traffic jams in crowded metro-cities during nights

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