Which of the following is a correct sequence of decreasing order of number of species ?

Options

A. a) Aves,pisces,reptiles,amphibians,mammals
B. b) Pisces,aves,reptiles,mammals,amphibians
C. c) Pisces,mammals,reptiles,amphibians,aves
D. d) Amphibians,aves, pisces, mammals,reptiles

Answer

To determine the correct sequence of decreasing order of the number of species among the classes of the phylum Chordata, we will analyze the classes provided and arrange them accordingly.

### Step-by-Step Solution:

1. **Identify the Classes**: The classes we are considering from the phylum Chordata are:
- Pisces (fishes)
- Aves (birds)
- Reptiles
- Mammals
- Amphibians

2. **Research the Number of Species**: We need to understand the approximate number of species in each class:
- **Pisces**: This class has the least number of species compared to others.
- **Aves**: Birds have a higher number of species than fishes.
- **Reptiles**: They have a similar number of species to birds, but slightly fewer.
- **Mammals**: This class has more species than reptiles.
- **Amphibians**: This class has the highest number of species among the listed classes.

3. **Arrange in Decreasing Order**: Based on the information gathered:
- **Pisces** (least number of species)
- **Aves** (more than Pisces)
- **Reptiles** (similar to Aves but slightly fewer)
- **Mammals** (more than Reptiles)
- **Amphibians** (highest number of species)

Therefore, the correct sequence in decreasing order of the number of species is:
- Pisces < Aves < Reptiles < Mammals < Amphibians

4. **Evaluate Options**: Now, we need to evaluate the provided options:
- **Option A**: Aves followed by Pisces (Incorrect)
- **Option B**: Pisces followed by Aves, Reptiles, Mammals, Amphibians (Correct)
- **Option C**: Pisces followed by Mammals (Incorrect)
- **Option D**: Amphibians followed by Aves (Incorrect)

5. **Conclusion**: The correct answer is **Option B**: Pisces, Aves, Reptiles, Mammals, Amphibians.