Which of these is necessary for a wave to occur ?

Options

A. frequency
B. Instrument
C. Medium
D. Pitch

Answer

To determine what is necessary for a wave to occur, specifically for sound waves, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Waves**: Recognize that waves can be classified into different types, such as mechanical waves (like sound waves) and electromagnetic waves. For this question, we are focusing on mechanical waves, particularly sound waves.

2. **Identifying the Nature of Sound Waves**: Sound waves are mechanical waves, which means they require a medium to travel through. This medium can be a solid, liquid, or gas.

3. **Role of Medium**: The medium is essential for the propagation of sound waves. Sound travels through the medium by causing the molecules within it to vibrate. These vibrations are what allow sound to move from one point to another.

4. **Conclusion on Requirements**: Since sound waves cannot travel through a vacuum (where there is no medium), the presence of a medium is the most crucial requirement for sound waves to occur.

5. **Eliminating Other Options**: Other properties related to sound, such as frequency and pitch, are characteristics of sound waves but are not necessary for the wave to occur. They describe how sound behaves rather than the fundamental requirement for its existence.

6. **Final Answer**: Therefore, the correct answer to the question of what is necessary for a sound wave to occur is **medium**.