Assertion `:-` A block is hanged from spring. Spring force on block gravitational force on block are not action and reaction pair.
Reason `:-` Action and reaction force acts in opposite direction.

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion.
B. If both Assertion & Reason are True but Reason is not a correct explanation of the Assertiion.
C. If Assertion is True but the Reason is False.
D. If both Assertion & Reason are False

Answer

To solve the question, we need to analyze the assertion and the reason provided.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that a block is hung from a spring, and the spring force acting on the block and the gravitational force acting on the block are not action and reaction pairs.
- **Conclusion**: This assertion is true. The spring force (upward) and gravitational force (downward) are indeed not action-reaction pairs.

2. **Understanding the Reason**:
- The reason states that action and reaction forces act in opposite directions.
- **Conclusion**: This statement is also true. According to Newton's third law, for every action, there is an equal and opposite reaction.

3. **Analyzing Action-Reaction Pairs**:
- Action-reaction pairs must act on different objects. For example, if the block exerts a force on the spring, the spring exerts an equal and opposite force on the block.
- The gravitational force is the force exerted by the Earth on the block, while the spring force is the force exerted by the spring on the block. These forces are not acting on each other but rather on the same object (the block).

4. **Conclusion**:
- While both the assertion and the reason are true, the reason does not correctly explain why the assertion is true. The assertion is about the nature of the forces involved (spring force vs. gravitational force), while the reason discusses the general property of action-reaction pairs.

### Final Answer:
- Both the assertion and reason are true, but the reason is not the correct explanation of the assertion. Therefore, the correct option is B.