Which is incorrect ?

Options

A. Insects have three pairs of legs
B. Flame cells occur in platyhelminthes
C. Whale is the largest fish
D. All mammals have mammary glands , Hairs may be present.

Answer

To determine which statement is incorrect, let's analyze each option one by one:

1. **Insects have three pairs of legs.**
- This statement is correct. Insects, which belong to the class Insecta, are characterized by having three pairs of legs (totaling six legs), which is a defining feature of all insects.

2. **Flame cells occur in Platyhelminthes.**
- This statement is also correct. Flame cells are specialized excretory cells found in flatworms (Phylum Platyhelminthes). They help in the excretion of waste and maintaining osmotic balance.

3. **Whale is the largest fish.**
- This statement is incorrect. Whales are not fish; they are mammals. The largest whale, the blue whale, is the largest mammal, not the largest fish. Therefore, this statement is false.

4. **All mammals have mammary glands; hairs may be present.**
- This statement is correct. All mammals possess mammary glands, which are used to produce milk for feeding their young. While many mammals have hair, some may have reduced or no hair, but the presence of mammary glands is a defining characteristic of mammals.

Based on the analysis, the incorrect statement is:
- **Whale is the largest fish.**

### Summary of the Solution:
The incorrect statement is "Whale is the largest fish" because whales are mammals, not fish. All other statements are correct.