Chemical Process
Presence of carbonaceous matter in the sewage

Causes reduction in its dissolved oxygen content thereby endangering the life of aquatic creatures
Increases the quantity of chlorine used for its purification
Reduces sulphate ions to sulphides causing obnoxious smell
All of these

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Chemical Process
During the manufacture of sulphuric acid, the temperature of molten sulphur is not increased beyond 160°C, as

Its viscosity is not reduced on further heating (hence pressure drop on pumping it, cannot be further reduced)
It is very corrosive at elevated temperature
It decomposes on further increasing the temperature
None of these

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