Sound cannot travel through vacuum. It always require a medium to travel

Q cannot hear the sound produced by P when the medium between them is Vacuum.

Explanation:
When sound travels, it requires a medium to propagate or travel through. The medium can be any substance like air, water, solids, or liquids. However, in a vacuum, there is no medium present, as it is a space devoid of matter. Hence, sound waves cannot travel through a vacuum.

- Sound Waves:
Sound is a form of energy that travels in the form of waves. These waves are called sound waves. When a sound is produced, it creates vibrations in the air molecules, which then propagate as sound waves.

- Medium and Sound Propagation:
Sound waves require a medium to travel because they need molecules or particles to transfer the vibrations. In a medium like air, the sound waves transfer the energy by causing the air molecules to vibrate. These vibrations then travel from one particle to another, allowing the sound to propagate.

- Vacuum and Sound Propagation:
A vacuum, on the other hand, is a space devoid of any particles or molecules. Since there are no particles to vibrate or transfer the vibrations, sound waves cannot propagate through a vacuum. Therefore, Q cannot hear the sound produced by P when the medium between them is a vacuum.

- Other Options:
a) Oil: Sound can propagate through liquids such as oil, as they have molecules that can vibrate and transfer the sound waves.
b) Air: Sound can propagate through air, as it is a common medium for sound waves to travel.
c) Brick Wall: Sound can partially propagate through solids like brick walls, but it gets attenuated or weakened due to absorption and reflection.
d) Vacuum: Sound cannot propagate through a vacuum, as there are no particles or molecules to transfer the sound waves.

Hence, the correct answer is option 'D' - Vacuum.