Chemistry
The total energy of revolving electron in an atom

Cannot be negative
Can have any value above zero
Can never be positive
Will always be positive

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Chemistry
The open "Sigrees" or coal stoves often require fanning to sustain burning because of

Tendency of carbon dioxide to form a layer along with dust smoke
Lack of oxygen in the surroundings of sigrees
Accumulation of smoke and dust over the sigrees
Interrupted release of moisture from the material

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