The following substances are the exretory products in animals. Choose the least toxic from among them

Options

A. Urea
B. Uric acid
C. Ammonia
D. Carbon dioxide

Answer

To determine the least toxic excretory product among urea, uric acid, ammonia, and carbon dioxide, we can analyze each substance based on its toxicity and the organisms that excrete them.

### Step-by-Step Solution:

1. **Identify the Excretory Products**: The excretory products listed are urea, uric acid, ammonia, and carbon dioxide.

2. **Understand the Nature of Each Product**:
- **Ammonia**: This is highly toxic and requires a large amount of water to be excreted safely. It is primarily excreted by aquatic animals like fish.
- **Urea**: Less toxic than ammonia and requires less water for excretion. It is excreted by mammals, including humans, and is known as ureotelic excretion.
- **Uric Acid**: This is even less toxic than urea and is excreted as a paste with minimal water loss. It is typical in birds, reptiles, and terrestrial snails, classified as uricotelic organisms.
- **Carbon Dioxide**: While it is a waste product of respiration, it is not a nitrogenous waste and is not toxic in the same sense as the others. It is excreted in gaseous form through respiration.

3. **Compare the Toxicity**:
- Ammonia is the most toxic.
- Urea is less toxic than ammonia.
- Uric acid is less toxic than urea.
- Carbon dioxide is not toxic in the same way and is a normal metabolic waste product.

4. **Conclusion**: Among the given substances, **uric acid** is the least toxic excretory product. However, if we consider carbon dioxide as a non-toxic waste product, it could be argued that carbon dioxide is the least toxic overall.

### Final Answer:
The least toxic excretory product among the given options is **uric acid** (or carbon dioxide, if considering non-toxicity).