The least toxic nitrogenous waste is produced by

Options

A. Mammals and molluscs
B. Birds and lizards
C. Frog and cartilaginous fishes
D. Insects and bony fishes

Answer

To determine which group of organisms produces the least toxic nitrogenous waste, we need to analyze the types of nitrogenous waste produced by different organisms and their toxicity levels.

### Step-by-Step Solution:

1. **Identify Types of Nitrogenous Waste**:
- The three primary forms of nitrogenous waste are ammonia, urea, and uric acid.
- Ammonia is the most toxic and requires a large amount of water for excretion.
- Urea is less toxic than ammonia and requires less water for excretion.
- Uric acid is the least toxic and can be excreted with minimal water loss.

2. **Classify Organisms Based on Nitrogenous Waste**:
- **Ammonotelic**: Organisms that excrete ammonia (e.g., many bony fishes, aquatic amphibians).
- **Ureotelic**: Organisms that excrete urea (e.g., terrestrial amphibians, marine fishes).
- **Uricotelic**: Organisms that excrete uric acid (e.g., reptiles, birds, land snails, insects).

3. **Analyze the Options**:
- **Option A**: Mammals and mollusks - Mammals primarily excrete urea, and mollusks can vary.
- **Option B**: Birds and lizards - Both birds and lizards (reptiles) excrete uric acid, making them uricotelic.
- **Option C**: Frogs and cartilaginous fish - Frogs (amphibians) excrete urea, and cartilaginous fish also excrete urea.
- **Option D**: Insects and bony fish - Insects excrete uric acid, while bony fish excrete ammonia.

4. **Determine the Least Toxic Waste Producers**:
- Among the options, birds and lizards (Option B) are both uricotelic and produce uric acid, which is the least toxic form of nitrogenous waste.

5. **Conclusion**:
- The group of organisms that produces the least toxic nitrogenous waste is **Option B: Birds and lizards**.

### Final Answer:
**B: Birds and lizards**