Which of the following excreted in mammals in the form of nitrogen

Options

A. Ammonium oin
B. Ammonia
C. Uric acid
D. Urea

Answer

To solve the question "Which of the following is excreted in mammals in the form of nitrogen?", we need to analyze the options provided: Ammonium ion, Ammonia, Uric acid, and Urea.

### Step-by-Step Solution:

1. **Understand Nitrogenous Wastes**:
- There are three primary types of nitrogenous wastes produced by organisms: ammonia, urea, and uric acid. Each type is associated with different groups of organisms based on their habitat and physiology.

2. **Identify the Type of Organisms**:
- **Ammonia**: This is the most toxic form of nitrogenous waste and is primarily excreted by aquatic organisms (ammonotelic organisms) because it requires a large amount of water to dilute it.
- **Uric Acid**: This is excreted by organisms that can conserve water, such as birds and reptiles (uricotelic organisms). It is less toxic and requires less water for excretion.
- **Urea**: This is produced by terrestrial animals, including mammals, and is less toxic than ammonia. Organisms that excrete urea are known as ureotelic organisms.

3. **Focus on Mammals**:
- Mammals, including humans, are classified as ureotelic organisms. They convert ammonia into urea, which is then excreted.

4. **Evaluate the Options**:
- **Ammonium ion**: Incorrect, as mammals do not excrete ammonia directly.
- **Ammonia**: Incorrect, as mammals do not excrete ammonia due to its toxicity.
- **Uric acid**: Incorrect, as this is primarily excreted by birds and reptiles.
- **Urea**: Correct, as this is the form of nitrogenous waste excreted by mammals.

5. **Conclusion**:
- The correct answer is **Urea** (Option D).

### Final Answer:
**Urea** is excreted in mammals in the form of nitrogen.