Unknown Amount of residual chlorine to be present after contact time should: (Repeat 2013) A 0.5 mg/L B 1 mg/L C 1.5 mg/L D 2 mg/L 💡 Explanation Amount of residual chlorine to be present after contact time should: (Repeat 2013) ✓ Correct Answer: A. 0.5 mg/L