Which of the following cannot be accelerated by cyclotron ?

Options

A. Negative ions
B. Positive ions
C. Both A and B
D. Electrons

Explanation

To solve the question "Which of the following cannot be accelerated by a cyclotron?", we need to analyze the options given and understand the working principle of a cyclotron.

### Step-by-Step Solution:

1. **Understanding the Cyclotron**:
- A cyclotron is a type of particle accelerator that uses a magnetic field and electric field to accelerate charged particles, such as ions and electrons, to high speeds.

2. **Identifying the Options**:
- The options provided are:
- A) Negative ions
- B) Positive ions
- C) Both A and B
- D) Electrons

3. **Analyzing Each Option**:
- **Negative Ions (Option A)**: Cyclotrons can accelerate negative ions. These are particles that have gained one or more electrons and carry a negative charge.
- **Positive Ions (Option B)**: Cyclotrons can also accelerate positive ions. These are particles that have lost one or more electrons and carry a positive charge.
- **Both A and B (Option C)**: Since both negative and positive ions can be accelerated by a cyclotron, this option is incorrect.
- **Electrons (Option D)**: Electrons are negatively charged particles with very small mass. Due to their low mass, they move at very high velocities when subjected to the cyclotron's fields, which makes it difficult for the cyclotron to effectively accelerate them.

4. **Conclusion**:
- Based on the analysis, the cyclotron cannot effectively accelerate electrons due to their low mass and high velocity. Therefore, the correct answer is **Option D: Electrons**.

### Final Answer:
The correct option is **D) Electrons**.