In the treatment of water for municipal supply, chlorine is used to

Step 1: Analyze the question The question asks about the purpose of chlorine in municipal water treatment, which is the disinfection stage.

Step 2: Explain the concept Municipal water treatment usually follows these stages:

1. Screening/sedimentation: removes large debris and suspended solids.
2. Coagulation (e.g. alum) and filtration: removes fine particles and some colour.
3. Aeration/activated carbon: helps remove odour and taste.
4. Chlorination: kills disease-causing microorganisms such as bacteria, viruses and protozoa. This helps prevent waterborne diseases like cholera, typhoid and dysentery.
5. Fluoridation (in some places): helps prevent tooth decay.

Step 3: Check each option

• A. Prevent tooth decay: This is the job of fluoride, not chlorine.
• B. Prevent goitre: Goitre is caused by iodine deficiency, so it is prevented with iodine (iodised salt).
• C. Kill germs: Chlorine is a strong oxidising agent and disinfectant. It kills bacteria and other pathogens. ✔
• D. Remove colour or odour: Chlorine can slightly affect colour and odour, but this is not its main purpose. Activated carbon and aeration are the main methods for that.

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

Tip: Remember the pairing of substance and purpose:

• Chlorine → kills germs
• Fluoride → teeth
• Iodine → goitre
• Alum → coagulation (settles suspended particles)
• Activated carbon → removes taste, colour and odour