Protons and neutrons are bound in a nucleus by the

Options

A. short range 'weak interaction'
B. short range 'strong interaction'
C. long range 'electromagnetic interaction'
D. long range 'gravitational interaction'

Explanation

To answer the question "Protons and neutrons are bound in a nucleus by", we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Components of the Nucleus**:
- The nucleus of an atom is composed of protons and neutrons. Protons are positively charged particles, while neutrons have no charge.

2. **Identifying the Force that Binds Them**:
- Protons and neutrons are held together in the nucleus by a force. This force is essential for the stability of the nucleus.

3. **Recognizing the Type of Force**:
- The force that binds protons and neutrons together is known as the **strong nuclear force**. This force is one of the four fundamental forces of nature.

4. **Characteristics of the Strong Nuclear Force**:
- The strong nuclear force is:
- **Attractive**: It pulls protons and neutrons together.
- **Short-range**: It acts over very short distances, typically on the order of a femtometer (10^-15 meters).
- **Charge-independent**: It acts equally on protons and neutrons, regardless of their charge.

5. **Conclusion**:
- Therefore, the correct answer to the question is that protons and neutrons are bound in a nucleus by the **strong nuclear force**.

### Final Answer:
Protons and neutrons are bound in a nucleus by the **strong nuclear force**.

---