Assertion `:-` Mostly aquatic animals are ammonotelic.
Reason `:-` Ammonia is the most toxic form and requires large amount of water for its elimination.

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion .
B. If both Assertion & Reason are True but Reason is not a correct explanation of the Assertion
C. If Assertion is True but the Reason is False.
D. If both Assertion & Reason are false.

Answer

To solve the assertion and reason question, we will analyze both statements step by step.

### Step 1: Understanding the Assertion
The assertion states that "mostly aquatic animals are ammonotelic."
- **Explanation**: Ammonotelic organisms are those that excrete ammonia as their primary nitrogenous waste. This is common in aquatic animals such as bony fishes, aquatic amphibians, and some aquatic insects. These organisms live in water, which allows them to easily eliminate ammonia due to its high solubility in water.

### Step 2: Understanding the Reason
The reason states that "ammonia is the most toxic form and requires a large amount of water for its elimination."
- **Explanation**: Ammonia is indeed highly toxic to organisms. To safely excrete ammonia, aquatic animals need to dilute it with a significant amount of water. This is feasible in an aquatic environment where water is abundant. Ammonia can be excreted through diffusion across the body surface or gills, making it efficient for aquatic organisms.

### Step 3: Evaluating the Relationship
Now we need to evaluate whether the reason supports the assertion.
- Both statements are true:
- The assertion is correct because many aquatic animals are ammonotelic.
- The reason is also correct as ammonia is toxic and requires a lot of water for its elimination.
- The reason justifies the assertion because the need for water to excrete ammonia explains why aquatic animals adopt ammonotelism.

### Conclusion
Both the assertion and the reason are true, and the reason supports the assertion. Therefore, the correct answer is that both statements are true and the reason justifies the assertion.