Assertion (A) : Graphite is chemically more reactive than diamond .
Reason (R) : Diamond is very hard but fraphite si soof .

Options

A. If both (A) and (R) are correct and (R) is correct explanation of (A)
B. If both (A) and (R) are correct and (R) is not correct explanation of (A)
C. If (A) is correct , but (R) is incorrect
D. If (A) is incorrect but (R) is correct .

Explanation

To solve the assertion and reason question, we need to analyze both statements carefully.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that "Graphite is chemically more reactive than diamond."
- To evaluate this, we need to consider the structure and bonding of both graphite and diamond.

2. **Analyzing Graphite**:
- Graphite has a layered structure where carbon atoms are arranged in sheets.
- Each carbon atom in graphite is sp² hybridized and is bonded to three other carbon atoms, forming a planar structure.
- Importantly, graphite has delocalized π electrons due to the overlapping of p orbitals across the layers, which contributes to its chemical reactivity.

3. **Analyzing Diamond**:
- Diamond has a three-dimensional tetrahedral structure where each carbon atom is sp³ hybridized and bonded to four other carbon atoms.
- This structure results in strong covalent bonds with no delocalized electrons, making diamond very stable and less reactive compared to graphite.

4. **Conclusion on Assertion**:
- Since graphite has delocalized electrons and a structure that allows for chemical reactions, it is indeed more chemically reactive than diamond. Therefore, the assertion is **true**.

5. **Understanding the Reason (R)**:
- The reason states that "Diamond is very hard but graphite is soft."
- This statement is also correct. Diamond's hardness is due to its strong covalent bonds in a three-dimensional network, while graphite's layered structure allows it to be soft and slippery.

6. **Evaluating the Explanation**:
- While both the assertion and the reason are true, the reason does not explain why graphite is more reactive than diamond. The hardness and softness of the materials relate to their structural properties but do not directly account for their chemical reactivity.

7. **Final Conclusion**:
- Both the assertion and the reason are correct, but the reason is not the correct explanation for the assertion. Thus, the correct answer is that the assertion is true, and the reason is true but does not explain the assertion.

### Final Answer:
- Assertion (A) is true.
- Reason (R) is true, but it does not explain (A).
- Therefore, the correct option is **B**.