How many statements are incorrect :-
(a) Automobiles are major cause for atmospheric pollution atleast in metrocities.
(b) Water which contain 0.1% of impurities of sewage is harmful for drinking.
(c) As organic matter increased BOD decreases.
(d) High concentration of DDT affects Ca-metabolism in birds.

Options

A. One
B. Three
C. Two
D. Four

Answer

To determine how many statements are incorrect, let's analyze each statement one by one:

### Step 1: Analyze Statement (a)
**Statement (a):** Automobiles are a major cause of atmospheric pollution at least in metrocities.
- **Analysis:** This statement is correct. In metropolitan areas, the high population density leads to a significant number of automobiles, which contribute to air pollution.

### Step 2: Analyze Statement (b)
**Statement (b):** Water which contains 0.1% of impurities of sewage is harmful for drinking.
- **Analysis:** This statement is also correct. Even a small percentage of impurities, such as bacteria, nutrients, and other contaminants, can render water unsafe for human consumption.

### Step 3: Analyze Statement (c)
**Statement (c):** As organic matter increases, BOD decreases.
- **Analysis:** This statement is incorrect. Biological Oxygen Demand (BOD) measures the amount of oxygen required by microorganisms to decompose organic matter. As organic matter increases, BOD increases because more oxygen is needed for decomposition.

### Step 4: Analyze Statement (d)
**Statement (d):** High concentration of DDT affects Ca-metabolism in birds.
- **Analysis:** This statement is correct. High levels of DDT (a pesticide) can disrupt calcium metabolism in birds, leading to thinner eggshells and increased egg breakage.

### Conclusion
After analyzing all four statements:
- **Correct Statements:** (a), (b), and (d)
- **Incorrect Statement:** (c)

Thus, there is **1 incorrect statement**.

### Final Answer
**The number of incorrect statements is 1.**

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