Physics
Radio waves sent out by a radio stations are reflected by

Ionosphere
Mesosphere
Stratosphere
Troposphere

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Physics
Siphon will fail to work if:

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

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