Select the true statement.

Options

A. In fishes, kidney plays a major role in ammonia excretion.
B. Ammonia is 100,000 times less toxic than urea
C. Sharks retain a large amount of urea in the blood as a major osmolyte to balance the osmolarity of the body fluids.
D. Most terrestrial reptiles excrete ammonia.

Answer

To solve the question "Select the true statement," we will evaluate each of the provided statements one by one.

### Step-by-Step Solution:

1. **Evaluate the First Statement:**
- The statement is: "In fishes, the kidney plays a major role in ammonia excretion."
- **Analysis:** This statement is incorrect because in fishes, ammonia is primarily excreted through the gills, not the kidneys.

2. **Evaluate the Second Statement:**
- The statement is: "Ammonia is 1 lakh times less toxic than urea."
- **Analysis:** This statement is also incorrect. Ammonia is actually far more toxic than urea, making this statement false.

3. **Evaluate the Third Statement:**
- The statement is: "Sharks retain a large amount of urea in the blood as a major osmolite to balance the osmolarity of the body fluid."
- **Analysis:** This statement is correct. Sharks, being cartilaginous fish, use urea to help maintain osmotic balance in their bodies.

4. **Evaluate the Fourth Statement:**
- The statement is: "Most terrestrial reptiles excrete ammonia."
- **Analysis:** This statement is incorrect. Most terrestrial reptiles excrete uric acid, not ammonia, as their primary nitrogenous waste.

### Conclusion:
After evaluating all the statements, the true statement is the third one: "Sharks retain a large amount of urea in the blood as a major osmolite to balance the osmolarity of the body fluid."