Answer:

A.iodine

Explanation:

Iodine•advantages-forms brown color that indicates strength-not affected by hard water-less irritating to the skin than the chloride-activity not lost rapidly in the presence of organic matter•disadvantages-effectiveness decreases greatly with the increase in pH most active at pH 3.0-very low acting at ph 7.0-should not be used in water that is at 120°F or hot water-mike discolor equipment & services

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