Reverberation of sound is used in

Uses of reverberation of sound: Megaphones or loudhailers, horns, musical instruments such as trumpets and shehnais, are all designed to send sound in a particular direction without spreading it in all directions.

Reverberation is the reflection of sound waves off surfaces, which causes the sound to persist or echo in an enclosed space. This property is used in various devices to enhance sound quality or increase its reach.

Let’s analyze the options:

1. Stethoscope: Reverberation helps doctors listen to internal body sounds more clearly by amplifying and reflecting the sound inside the stethoscope's chest piece.
2. Trumpets: Trumpets use reverberation within the instrument's hollow body to amplify and project the sound. The sound waves bounce inside, enhancing the sound produced when the musician blows into it.
3. Megaphone: A megaphone works by using the principle of reverberation, directing and amplifying the sound waves toward the listener, ensuring the voice travels over a larger area.

Conclusion:

Since reverberation is used in all of these devices to enhance or project sound, the correct answer is d) All of these.