Question

The WHO standard of drinking water is

• A. 20 mg NO$_3^-$ - N/L
• B. 10 mg NO$_3^-$ - N/L
• C. 30 mg NO$_3^-$ - N/L
• D. 50 mg NO$_3^-$ - N/L

Hint:

WHO drinking water standard:
- 10 mg NO$_3^-$ - N/L.
- Prevents methemoglobinemia in infants.
- Also expressed as 50 mg NO$_3^-$/L.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
This question tests knowledge of water quality standards set by the World Health Organization (WHO).

Step 2: Detailed Explanation:
The WHO standard for drinking water is 10 mg NO$_3^-$ - N/L (B).
This is the maximum allowable concentration of nitrate-nitrogen in drinking water.
Exceeding this limit can cause methemoglobinemia (blue baby syndrome) in infants.
Other standards:
- 20 mg NO$_3^-$ - N/L (A): Not a standard.
- 30 mg NO$_3^-$ - N/L (C): Not a standard.
- 50 mg NO$_3^-$ - N/L (D): This is the standard for nitrate ion (NO$_3^-$), not nitrate-nitrogen.
Note: 50 mg NO$_3^-$/L is equivalent to approximately 11.3 mg NO$_3^-$ - N/L.
Thus, the WHO standard is 10 mg NO$_3^-$ - N/L.

Step 3: Final Answer:
Thus, the WHO standard for drinking water is 10 mg NO$_3^-$ - N/L, which corresponds to option (B).
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