$ Plastids occur in plant cells and animals cells.
! Centriols are present only in plant cells.

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

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that "plastids occur in plant cells and animal cells." We need to analyze whether this statement is true or false.
- **Plastids** are organelles found in plant cells that are involved in the synthesis and storage of food. They are primarily responsible for photosynthesis (in chloroplasts), storage of starch (in amyloplasts), and synthesis of pigments (in chromoplasts).
- **Conclusion**: Plastids are present only in plant cells and not in animal cells. Therefore, the assertion is **false**.

2. **Understanding the Reason**: The reason states that "centrioles are present only in plant cells." We need to determine the accuracy of this statement.
- **Centrioles** are cylindrical structures found in animal cells that play a crucial role in cell division, particularly in the formation of spindle fibers that separate chromosomes during mitosis.
- In contrast, plant cells do not have centrioles; instead, they have other structures that help in cell division.
- **Conclusion**: Centrioles are present in animal cells and absent in plant cells. Therefore, the reason is also **false**.

3. **Final Conclusion**: Since both the assertion and the reason are false, we can conclude that the correct option is that both the assertion and the reason are incorrect.