The pH of water sample collected from a river was found to be acidic in the range of 3.5 – 4.5. On the banks of the river were several factories that were discharging effluents into the river. The effluents of which one of the following factories is the most likely cause for lowering the pH of river water?
(a) Soap factory
(b) Detergent factory
(c) Alcohol distillery
(d) Plastic cup manufacturing factory
