Physics
Siphon will fail to work if:

The densities of the liquid in the two vessels are equal.
Both its limbs are of unequal length.
The level of the liquid in the two vessels are at the same height.
The temperature of the liquids in the two vessels are the same.

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Physics
The earth is a

Good absorber and good radiator of heat
Good reflector of heat
Non-absorber of heat
Bad absorber and bad radiator of heat

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