Which excretory material is least toxic ?

Options

A. Ammonia
B. Urea
C. Uric acid
D. All are equally toxic

Answer

To determine which excretory material is least toxic, we need to analyze the three main types of nitrogenous wastes produced by organisms: ammonia, urea, and uric acid.

### Step-by-Step Solution:

1. **Identify the Types of Nitrogenous Wastes**:
- The three primary types of nitrogenous wastes are:
- Ammonia
- Urea
- Uric Acid

2. **Assess the Toxicity of Each Waste**:
- **Ammonia**:
- Ammonia is the most toxic form of nitrogenous waste. It is highly soluble in water and requires a large amount of water to be excreted safely. Organisms that excrete ammonia are known as ammonotelic organisms, typically found in aquatic environments.
- **Urea**:
- Urea is less toxic than ammonia. It is produced in the liver and requires less water for excretion compared to ammonia. Organisms that excrete urea are called ureotelic organisms, which include mammals and some amphibians.
- **Uric Acid**:
- Uric acid is the least toxic of the three. It is excreted as a semi-solid paste, which conserves water, making it advantageous for organisms in arid environments. Organisms that excrete uric acid are known as uricotelic organisms, such as birds and reptiles.

3. **Conclusion**:
- Based on the toxicity levels, we conclude that uric acid is the least toxic nitrogenous waste. Therefore, the answer to the question "Which excretory material is least toxic?" is **uric acid**.

### Final Answer:
The least toxic excretory material is **uric acid**.