Question

According to drinking water standards, the desirable residual chlorine at the consumer end is about

• A. \(0.05\ \mathrm{mg/L}\)
• B. \(1.5\ \mathrm{mg/L}\)
• C. \(0.2-0.5\ \mathrm{mg/L}\)
• D. \(5\ \mathrm{mg/L}\)

Hint:

Recommended residual chlorine: \[ \boxed{ 0.2-0.5\ \mathrm{mg/L} } \] at the consumer end after at least 30 minutes of contact time.

Answer 1

The Correct Option is C

Step 1: Think about why chlorine is kept in drinking water.
A small amount of chlorine is deliberately left in treated water so it keeps protecting against germs all the way to the consumer's tap.
Step 2: Recall the standard range.
Drinking water standards recommend maintaining this residual chlorine between about 0.2 and 0.5 mg/L at the point of use.
Step 3: Check this against the options.
Values like 0.05 mg/L are too low to be effective and 1.5 or 5 mg/L are far too high and would affect taste and safety, so the correct range is 0.2 to 0.5 mg/L.
\[ \boxed{0.2 - 0.5\ \text{mg/L}} \]