Physics
On a cold day when a room temperature is 15oC, the metallic cap of a pen becomes much colder than its plastic body, though both are at the same temperature of 15oC, because

metals have higher thermal capacity than plastics
plastics have a higher thermal conductivity than metals
plastics have a lower density than metals
metals are good conductor of heat

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

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

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