Objective Question & Answer

Hardness as CaCO₃: Acceptable and desirable limits for general domestic and potable water

hardness typically range between 75 to 115 ppm (mg/L).

Turbidity (on silica scale): The permissible limit for drinking water is generally limited to 10 ppm (or 5–10 NTU), making option (a) incorrect.

Color (on cobalt/platinum-cobalt scale): The maximum permissible color for domestic supplies is typically 5 to 20 TCU/ppm (often capped at 5 to 10 ppm for acceptable standards and 15 max), making 15–25 ppm in option (b) outside standard ideal/permissible limits.

BOD (Biochemical Oxygen Demand): Potable domestic water should have a BOD of 0 ppm, as any measurable biological oxygen demand indicates organic contamination.