Which of the following statement (s) is (are) correct ?

Options

A. The rest mass of a stable nucleus is less than the sum of the rest masses of its separated nucleons.
B. The rest mass of a stable nucleus is greater than the sum of the rest masses of its separated nucleons.
C. In nuclear fission, energy is released by fusing two nuclei of medium mass (approximately 100 a.m.u.)
D. In nuclear fission, energy is released by fragammentation of a very heavy nulceus.

Explanation

To solve the question, we need to analyze each statement regarding nuclear physics and determine which ones are correct.

### Step-by-Step Solution:

1. **Understanding Mass in Nuclear Reactions**:
- In nuclear fission, a heavy nucleus splits into smaller nuclei. The mass of the original nucleus (A) is typically less than the combined mass of the resulting smaller nuclei (B and C). This is due to the mass-energy equivalence principle (E=mc²), where the lost mass is converted into energy.

**Hint**: Recall that in nuclear reactions, mass is not conserved in the traditional sense; instead, mass can be converted into energy.

2. **Analyzing Statement 1**:
- The first statement claims that the rest mass of a stable nucleus is less than the sum of the rest masses of the separated nuclei. This aligns with our understanding of fission, where the mass defect results in energy release.
- **Conclusion**: This statement is **correct**.

**Hint**: Think about the concept of mass defect and how energy is released during fission.

3. **Analyzing Statement 2**:
- The second statement asserts that the rest mass of a stable nucleus is greater than the sum of the rest masses of the separated nuclei. This contradicts the principle we established in step 1.
- **Conclusion**: This statement is **incorrect**.

**Hint**: Compare this statement with the first one and see how they contradict each other.

4. **Analyzing Statement 3**:
- The third statement discusses nuclear fusion, stating that energy is released by fusing two nuclei of medium mass (approximately 100 AMU). However, fusion typically occurs with light nuclei (like hydrogen isotopes) rather than medium mass nuclei.
- **Conclusion**: This statement is **incorrect**.

**Hint**: Recall the types of nuclei involved in fusion reactions and their typical mass ranges.

5. **Analyzing Statement 4**:
- The fourth statement claims that in nuclear fusion, energy is released by the fragmentation of a very heavy nucleus. This is misleading because fusion involves combining light nuclei rather than fragmenting heavy ones. However, if we interpret "fragmentation" loosely, it could refer to the process of forming a heavier nucleus from lighter ones.
- **Conclusion**: This statement is **correct** if we consider the context of fusion leading to the formation of heavier nuclei.

**Hint**: Consider the process of fusion and how it relates to the formation of heavier elements.

### Final Conclusion:
- The correct statements are **1 and 4**.

### Summary of Correct Statements:
1. The rest mass of a stable nucleus is less than the sum of the rest masses of the separated nuclei.
4. In nuclear fusion, energy is released by the combination of lighter nuclei to form a heavier nucleus.