which one of the following statements is correct ?

Options

A. Cyanobacteria such as Anabaena and Nostoc are inportant mobilzers of phosphates and potassium for plant nutrition in soil
B. At present , it is not possible to grow maize without chemical fertilizers.
C. Extensive use of chemical fertilizers may lead to eutrophication of nearby water bodies .
D. both Azotobacter and rhizbium fix atmospheric nitrogen in the nodules of plants .

Answer

To determine which statement is correct among the given options, we will analyze each statement one by one:

### Step 1: Analyze Statement A
**Statement A:** "Cyanobacteria, including Anabena and Nostoc, are important mobilizers of phosphates and potassium for plant nutrition in the soil."

- **Analysis:** Cyanobacteria, such as Anabena and Nostoc, are indeed important for nitrogen fixation due to their specialized cells called heterocysts. However, they do not primarily mobilize phosphates and potassium. Instead, they contribute nitrogen to the soil, which is essential for plant nutrition. Therefore, this statement is **incorrect**.

### Step 2: Analyze Statement B
**Statement B:** "At present, it is not possible to grow maize without chemical fertilizers."

- **Analysis:** This statement implies that maize cannot be grown without the use of chemical fertilizers. However, it is indeed possible to grow maize using organic manures and compost. Organic farming practices allow for the cultivation of maize without reliance on chemical fertilizers. Thus, this statement is also **incorrect**.

### Step 3: Analyze Statement C
**Statement C:** "Extensive use of chemical fertilizers may lead to eutrophication of the nearby water bodies."

- **Analysis:** This statement is accurate. The extensive use of chemical fertilizers can lead to runoff into nearby water bodies, causing nutrient pollution. This nutrient influx can result in algal blooms, a phenomenon known as eutrophication, which depletes oxygen in the water and harms aquatic life. Therefore, this statement is **correct**.

### Step 4: Analyze Statement D
**Statement D:** "Both Azotobacter and Rhizobium fix atmospheric nitrogen in the nodules of the plants."

- **Analysis:** Azotobacter is a free-living nitrogen-fixing bacterium found in the soil, while Rhizobium forms symbiotic relationships with leguminous plants and fixes nitrogen in root nodules. The statement incorrectly suggests that both fix nitrogen in nodules, which is not true for Azotobacter. Hence, this statement is **incorrect**.

### Conclusion
After analyzing all four statements, the correct statement is **Statement C**: "Extensive use of chemical fertilizers may lead to eutrophication of the nearby water bodies."

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