Chlorine is used in water purification because it

Step 1: Analyze the question The question asks why chlorine is added to water during purification. We need the main purpose of chlorination.

Step 2: The concept When chlorine dissolves in water, it forms hypochlorous acid (HOCl) and hydrochloric acid:

Cl₂ + H₂O → HCl + HOCl

Hypochlorous acid is a strong oxidizing agent. It penetrates the cell walls of microorganisms and disrupts their enzymes, killing them. This is called disinfection. It is how water treatment plants make water safe from diseases like cholera, typhoid and dysentery.

Step 3: Evaluate each option

• A. Bleaches impurities: Chlorine does have bleaching action, but that is not the main reason for using it in water treatment.
• B. Decolorizes water: This is a side effect, not the primary purpose.
• C. Destroys bacteria: This is the main purpose of chlorination, which is to kill disease-causing microorganisms. ✔
• D. Extremely soluble in water: Chlorine is only moderately soluble, and solubility is not the reason it is used.
• E. Pleasant tasting: False. Chlorine gives water a noticeable taste and smell.

Step 4: Answer The correct option is **C.

Tip: Remember "Chlorine = Clean and Kill germs." In water treatment, chlorine is the disinfectant. Whenever you see "purification" with chlorine, think "kills bacteria/germs."