Fuels and Combustion
As time passes, the calorific value of stored coal

Remains unaltered
Increases
May increase or decrease (depends on the method of storage)
Decreases

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Fuels and Combustion
Froth floatation is used for

Washing fine coal dust (< 0.5 mm size)
All of these
Washing lump coal (> 80 mm size)
Removing ash from the coal based on difference in specific gravity of coal and ash

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