Which one of the following categories of animals, is correctly described with no single exception in it ?

Options

A. All reptiles possess scales, have a three chambered heart and are cold blooded (poikilothermal)
B. All bony fishes have four pairs of gills and an operculum on each side
C. All sponges are marine and have collared cells
D. All mammals are viviparous and possess diaphragm for breathing.

Answer

To solve the question regarding which category of animals is correctly described with no exceptions, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Option A: All reptiles possess scales, have a three-chambered heart, and are cold-blooded.**
- **Analysis:** While it is true that most reptiles have scales and are cold-blooded, there are exceptions. For example, some reptiles like crocodiles have a four-chambered heart. Therefore, this statement is not universally true.

2. **Option B: All bony fishes have four pairs of gills and an operculum on each side.**
- **Analysis:** Bony fishes (Osteichthyes) typically have a pair of gills on each side, covered by an operculum. They do not have four pairs of gills; instead, they have one pair of gills on each side (two gills total). However, this option is the closest to being universally applicable since all bony fishes do have gills and opercula, but the number stated is incorrect.

3. **Option C: All sponges are marine and have collar cells.**
- **Analysis:** While most sponges are marine, there are freshwater sponges as well. Therefore, this statement is also not universally true.

4. **Option D: All mammals are viviparous and possess a diaphragm for breathing.**
- **Analysis:** This statement is incorrect because there are mammals, such as monotremes (e.g., the platypus), that are oviparous (egg-laying) and do not possess a diaphragm.

### Conclusion:
After analyzing all options, we find that **none of the statements are completely correct without exceptions**. However, if we consider the closest option, **Option B** is the most accurate regarding bony fishes, as they do possess gills and opercula, even though the number of gills stated is incorrect.

### Final Answer:
**The correct option is B: All bony fishes have four pairs of gills and an operculum on each side.**