Social & Preventive Medicine Residual chlorine in chlorination of water should be – A 1 mg/1 after 1 hr B 0.5 mg/1 after 1 hr C 1 mg/1 after 30 mins D 0.5 mg/1 after 30 mins 💡 Explanation Residual chlorine in chlorination of water should be – ✓ Correct Answer: B. 0.5 mg/1 after 1 hr