$ Obelia has three types of zooids namely (i) polyps (ii) Balastostyles (iii) Medusae
! The occurrence of more than one forms in an individual is called polymorphisms.

Options

A. If both As and R are correct and R is correct explanation of As
B. If both As and R are correct but R is not correct explanation of As
C. If As is correct, R is wrong
D. If both As and R are wrong.

Answer

To solve the question regarding Obelia and its types of zooids, we will follow these steps:

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "Obelia has three types of zooids namely polyps, blastostyles, and medusae."
- We need to confirm if this statement is true.

2. **Identifying the Types of Zooids**:
- Identify the three types of zooids in Obelia:
- **Polyps**: These are the feeding and asexual reproductive forms.
- **Blastostyles**: These are involved in budding and asexual reproduction.
- **Medusae**: These are the sexual forms that reproduce sexually.

3. **Conclusion on the Assertion**:
- Since all three types of zooids are indeed present in Obelia, the assertion is true.

4. **Understanding the Reason**:
- The reason states that "the occurrence of more than one form in an individual is called polymorphism."
- We need to verify if this definition of polymorphism is correct.

5. **Defining Polymorphism**:
- Polymorphism refers to the existence of multiple forms or morphs within a species or individual.
- In the case of Obelia, the presence of polyps, blastostyles, and medusae exemplifies polymorphism.

6. **Conclusion on the Reason**:
- Since the definition provided in the reason is accurate, the reason is also true.

7. **Evaluating the Relationship**:
- Now we need to check if the reason correctly explains the assertion.
- The reason explains that the presence of different forms (zooids) in Obelia is an example of polymorphism, which directly relates to the assertion that Obelia has these forms.

8. **Final Answer**:
- Both the assertion and reason are correct, and the reason is the correct explanation of the assertion. Therefore, the correct option is:
- **Option A**: Both Assertion and Reason are correct, and R is the correct explanation of the assertion.