Which of the following is not an inorganic impurity present in sewage?

Options

A. nitrate
B. phosphate
C. urea
D. metal salt

Answer

To determine which of the following is not an inorganic impurity present in sewage, we need to identify the types of impurities typically found in sewage and categorize them as either inorganic or organic.

### Step-by-Step Solution:

1. **Understand the Types of Impurities**:
- Sewage contains both inorganic and organic impurities.
- Inorganic impurities include substances like nitrates, phosphates, and metal salts.
- Organic impurities include substances like human feces, urea, animal waste, and organic matter from fruits and vegetables.

2. **Identify the Given Options**:
- The options provided are likely to include nitrates, phosphates, metal salts, and possibly urea or other organic substances.

3. **Classify Each Option**:
- **Nitrates**: These are inorganic compounds typically found in sewage.
- **Phosphates**: These are also inorganic compounds present in sewage.
- **Metal Salts**: These are inorganic impurities found in sewage.
- **Urea**: This is an organic compound that is a product of human metabolism and is found in urine.

4. **Determine the Answer**:
- Since nitrates, phosphates, and metal salts are all inorganic impurities, the one that is not an inorganic impurity is **urea**.

5. **Conclusion**:
- The answer to the question "Which of the following is not an inorganic impurity present in sewage?" is **urea**.