Pick out the correct statement from the following

Options

A. Energy released per unit mass of the reactant is less in case of fusion reaction
B. parcking fraction may be postitive or may be negative
C. `Pu^(239)` is not suitable for a fission reaction
D. for stable nucleus , the specific bonding energy is low

Explanation

To solve the problem of identifying the correct statement from the given options, let's analyze each statement step by step.

### Step-by-Step Solution:

1. **Understanding Fusion Reactions**:
- Fusion reactions typically involve the combination of lighter nuclei to form a heavier nucleus.
- These reactions generally release energy, but the statement claims that the energy released per unit mass of the reactant is less in fusion reactions. This is misleading because fusion reactions usually release a significant amount of energy.

**Conclusion**: This statement is incorrect.

**Hint**: Recall the nature of fusion reactions and their energy characteristics.

2. **Packing Fraction**:
- The packing fraction is defined as the mass defect divided by the number of nucleons (A).
- The mass defect can be positive or negative, depending on the binding energy of the nucleus. Therefore, the packing fraction can also be positive or negative.

**Conclusion**: This statement is correct.

**Hint**: Review the definition of packing fraction and its relationship with mass defect.

3. **Plutonium-239 and Fission**:
- Fission reactions typically involve heavier nuclei. Plutonium-239 is indeed a heavy nucleus and is suitable for fission reactions.
- The statement claims that plutonium-239 is not suitable for fission, which is incorrect.

**Conclusion**: This statement is incorrect.

**Hint**: Consider the characteristics of nuclei that undergo fission.

4. **Specific Binding Energy and Stability**:
- For a stable nucleus, the specific binding energy is actually high. A higher binding energy indicates that the nucleus is more stable.
- The statement claims that for a stable nucleus, the specific binding energy is low, which is incorrect.

**Conclusion**: This statement is incorrect.

**Hint**: Think about the relationship between binding energy and nuclear stability.

### Final Conclusion:
After analyzing all the statements, the only correct statement is about the packing fraction (Option B).

### Summary:
- Option A: Incorrect (fusion releases energy).
- Option B: Correct (packing fraction can be positive or negative).
- Option C: Incorrect (plutonium-239 is suitable for fission).
- Option D: Incorrect (stable nuclei have high binding energy).

Thus, the correct answer is **Option B**.