[A] : In frog skull is dicondyiic.
[R]: Skull articulates with the atlas vertebra by two occipital condyles one on each exoccipital.

Options

A. If both A and R are true and R is the correct explanation of A
B. If both A and R are true but R is not the correct explanation of A
C. If A is true and R is false
D. If both A and R are false

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that the frog skull is dicondylic. This means that the skull has two occipital condyles, which are rounded protuberances located at the posterior end of the skull.

2. **Identifying the Occipital Condyles**:
- The occipital condyles are the two small, rounded structures that allow the skull to articulate with the first cervical vertebra, known as the atlas. This articulation is crucial for the movement of the head.

3. **Explaining the Reason**:
- The reason provided states that the skull articulates with the atlas vertebra by these two occipital condyles, which are located on each exoccipital bone. This is an anatomical fact that supports the assertion.

4. **Connecting the Assertion and Reason**:
- Since the assertion is that the frog skull is dicondylic, and the reason explains how this structure allows for articulation with the atlas vertebra, both statements are true and directly related.

5. **Conclusion**:
- Therefore, both the assertion (A) and the reason (R) are true, and R correctly explains A.

### Final Answer:
Both A and R are true, and R is the correct explanation of A.

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