Q.

To keep the water safe against pathogenetic bacteria the residual chlorine should remain between

A. 10 ppm to 20 ppm
B. 1 ppm to 2 ppm
C. 0.2 to 0.8 ppm
D. 0.05 to 0.2 ppm
E. 6 ppm to 10 ppm
Answer» D. 0.05 to 0.2 ppm
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