Which of the following particles is not deflected by a magnetic field?

Options

A. Proton
B. Neutron
C. Electron
D. All of these

Explanation

To determine which particle is not deflected by a magnetic field, we need to analyze the properties of the particles in question. The key factor that influences whether a particle is deflected in a magnetic field is its electric charge.

### Step-by-Step Solution:

1. **Understand the Effect of Magnetic Fields on Charged Particles**:
- A charged particle experiences a force when it moves through a magnetic field. The force can be calculated using the formula:
\[ F = Q \cdot v \cdot B \]
where \( F \) is the force, \( Q \) is the charge of the particle, \( v \) is the velocity, and \( B \) is the magnetic field strength.

2. **Identify the Particles**:
- The question typically involves particles such as protons, neutrons, and electrons.
- **Proton**: A proton has a positive charge.
- **Neutron**: A neutron is neutral and has no charge.
- **Electron**: An electron has a negative charge.

3. **Analyze Each Particle**:
- **Proton**: Since it has a positive charge, it will be deflected by a magnetic field.
- **Neutron**: Since it is neutral (no charge), it will not be deflected by a magnetic field.
- **Electron**: Since it has a negative charge, it will also be deflected by a magnetic field.

4. **Conclusion**:
- Among the particles listed, the neutron is the only particle that is not deflected by a magnetic field because it has no charge.

### Final Answer:
- The particle that is not deflected by a magnetic field is the **neutron**.