Question

Which one of the following statements is (are) true?

• A. pH of acid rain is <5.6
• B. Concentration of DO below 6 ppm is good for the growth of fish.
• C. Clean water would have a BOD value of less than 5 ppm,
• D. Fertilizer contains phosphates which enhances algae growth on addition in water.

Answer 1

Answer: (A), (C), (D)

Statements A, C, and D are true.

Answer 2

We evaluate each statement:

A. pH of acid rain is <5.6. Normal rainwater has a pH of around 5.6 due to dissolved carbon dioxide. Acid rain is defined as precipitation with a pH lower than that of normal rainwater. Thus, this statement is true.

B. Concentration of DO below 6 ppm is good for the growth of fish. Dissolved Oxygen (DO) is essential for aquatic life. Most fish require DO levels significantly higher than 6 ppm for healthy growth and survival. Levels below 6 ppm are generally considered stressful and indicative of pollution. Thus, this statement is false.

C. Clean water would have a BOD value of less than 5 ppm. Biochemical Oxygen Demand (BOD) is a measure of the organic pollution in water. Clean water has low organic content, resulting in low oxygen consumption by microorganisms for decomposition. A BOD value of less than 5 ppm is typically considered characteristic of clean water. Thus, this statement is true.

D. Fertilizer contains phosphates which enhances algae growth on addition in water. Fertilizers contain nutrients like phosphates and nitrates. When these enter water bodies, they act as nutrients for algae, leading to excessive growth known as eutrophication or algal blooms. Thus, this statement is true.

Statements A, C, and D are true.

Explanation:

A: Acid rain is defined by a pH lower than normal rain (~5.6).

B: DO levels below 6 ppm are detrimental to most fish species.

C: Low BOD (<5 ppm) indicates minimal organic pollution, characteristic of clean water.

D: Phosphates from fertilizers are nutrients that promote excessive algal growth (eutrophication) in water bodies.