Physics
The layer of atmosphere used for radio-wave transmission is

Chromosphere
Stratosphere
Troposphere
Ionosphere

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Physics
It is easier to roll a stone up a sloping road than to lift it vertical upwards because

Work done in rolling a stone is less than in lifting it.
Work done in rolling is more than in lifting.
Work done in both is same but the rate of doing work is less in rolling.
Work done in lifting the stone is equal to rolling it.

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Physics
Superconductors are those elements

Whose conductivity is intermediate between metals and insulators
Which turn into insulators at very low temperatures
Which conduct electricity only at super-high temperatures
Whose resistance falls almost to zero at very low temperatures

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