Physics
Skating on ice is possible because

The pressure on the ice due to skate melts the ice by lowering its melting point forming a thin film of water
Ice is cold
The pressure on the ice due to skate raises its melting point
The surface of ice is smooth

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Physics
Superconductors are substances which

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

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Physics
The blue colour of water in the sea is due to

Reflection of blue light by impurities in sea water
Reflection of blue sky by sea water
Absorption of other colours except blue by water molecules
Scattering of blue light by water molecules

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