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

Explanation

To determine the least toxic excretory product among the given options (urea, uric acid, ammonia, and carbon dioxide), we can analyze each substance based on its toxicity and the form in which it is excreted by animals.

### Step-by-Step Solution:

1. **Understanding the Excretory Products**:
- **Ammonia**: This is the most toxic nitrogenous waste product. It is highly soluble in water and requires a large amount of water for its excretion. Animals that excrete ammonia, such as many aquatic organisms, do so because they have access to abundant water.

- **Urea**: Urea is less toxic than ammonia. It is produced in the liver through the urea cycle and is excreted in urine. While it is less toxic than ammonia, its accumulation can still be harmful to the body.

- **Uric Acid**: Uric acid is the least toxic of the nitrogenous wastes. It is produced by organisms such as birds, reptiles, and insects. Uric acid is excreted in a semi-solid form, which conserves water, making it advantageous for organisms in arid environments.

- **Carbon Dioxide**: While carbon dioxide is a waste product of respiration, it is not a nitrogenous waste. It is excreted through the lungs and is not toxic in the same way as nitrogenous wastes.

2. **Comparing Toxicity**:
- Among the substances listed, ammonia is the most toxic, followed by urea. Uric acid is less toxic than both ammonia and urea. Carbon dioxide is not classified as a nitrogenous waste and is not toxic in the same context.

3. **Conclusion**:
- Based on the analysis, the least toxic excretory product among the options provided is **uric acid**.

### Final Answer:
**Uric acid** is the least toxic excretory product among the given options.