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Identify the statement that is incorrect.

1. In cold water, dissolved oxygen (DO) may be as high as 10 ppm.
2. Pure water typically shows a BOD value of 5 ppm.
3. A lack of fluoride in drinking water is harmful, so soluble fluoride is often added to raise its level to about 1 ppm.
4. Rainwater is termed acid rain when its pH is above 6.5.

Correct answer: Rainwater is termed acid rain when its pH is above 6.5.

Solution

Option D is incorrect because rainwater is classified as acid rain when its pH is below 5.6, not above 6.5, indicating a higher acidity level.

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