Which of the following is not an electromagnetic wave?

Options

A. X-rays
B. `gamma`-rays
C. `beta`-rays
D. Heat rays

Answer

To determine which of the following options is not an electromagnetic wave, we need to understand what constitutes electromagnetic waves and identify the options provided.

### Step-by-Step Solution:

1. **Understanding Electromagnetic Waves**:
- Electromagnetic waves are waves that consist of oscillating electric and magnetic fields and travel through space at the speed of light. They include a wide range of frequencies known as the electromagnetic spectrum.

2. **Identifying Types of Electromagnetic Waves**:
- The electromagnetic spectrum includes various types of waves such as:
- Radio waves
- Microwaves
- Infrared rays
- Visible light
- Ultraviolet rays
- X-rays
- Gamma rays

3. **Analyzing the Options**:
- We need to check the options given in the question to see which one does not belong to the electromagnetic spectrum.
- Common terms that may appear include:
- X-rays (electromagnetic wave)
- Gamma rays (electromagnetic wave)
- Beta rays (not an electromagnetic wave)
- Heat rays (often referred to as infrared radiation, which is an electromagnetic wave)

4. **Conclusion**:
- Among the options, beta rays are not classified as electromagnetic waves. They are a type of radiation emitted when an electron is released, and they are known as beta radiation. Therefore, the correct answer is that beta rays are not an electromagnetic wave.

### Final Answer:
Beta rays are not an electromagnetic wave.