[A] : Tympanic membrane stretching across the aperture between skull bones or within an external meatus.
[B]: This vibrates periodically and transmit- ting external air pressure changes to ear os- sicles of middle ear.

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

To solve the question, we need to analyze the two statements provided:

**Statement A**: "Tympanic membrane stretching across the aperture between skull bones or within an external meatus."
**Statement B**: "This vibrates periodically and transmits external air pressure changes to ear ossicles of the middle ear."

### Step-by-Step Solution:

1. **Understanding Statement A**:
- The tympanic membrane, commonly known as the eardrum, is indeed located in the ear. It stretches across the external auditory canal (external meatus) and separates the outer ear from the middle ear.
- The assertion mentions that it stretches between skull bones, which is somewhat misleading. While the tympanic membrane is located near the skull, it does not stretch between skull bones directly; instead, it is positioned within the external auditory canal.

**Conclusion for A**: Statement A is partially correct but misleading in its phrasing.

2. **Understanding Statement B**:
- The tympanic membrane does vibrate in response to sound waves. These vibrations occur periodically as sound waves hit the membrane.
- When the tympanic membrane vibrates, it transmits these vibrations to the ossicles of the middle ear (malleus, incus, and stapes), which then amplify the sound and transmit it to the inner ear.

**Conclusion for B**: Statement B is correct.

3. **Final Evaluation**:
- Since Statement A is misleading and not entirely correct, while Statement B is correct, we conclude that:
- Statement A is false.
- Statement B is true.

### Final Answer:
- **A is false, B is true**.