Graphite is used as anode but diamond is not.
There exist free electrons between two parallel sheets of graphite, hence it helps in electrode conduction.

Options

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

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question states that graphite is used as an anode while diamond is not, and it asks for an explanation regarding this difference based on their electronic structures.

2. **Analyzing Graphite**:
- Graphite consists of carbon atoms arranged in layers of hexagonal structures.
- Each carbon atom in graphite is bonded to three other carbon atoms through covalent bonds, using three of its four valence electrons.
- The fourth electron from each carbon atom is free to move between the layers, creating a "sea of electrons."

3. **Conductivity of Graphite**:
- The presence of these free electrons allows graphite to conduct electricity effectively.
- The delocalization of these electrons between the layers enables graphite to act as a good conductor, similar to metals.

4. **Analyzing Diamond**:
- In contrast, diamond has a tetrahedral structure where each carbon atom is bonded to four other carbon atoms using all four of its valence electrons.
- This arrangement results in a strong covalent network with no free electrons available for conduction.

5. **Conductivity of Diamond**:
- Since all the electrons in diamond are involved in bonding, there are no free electrons to facilitate electrical conduction.
- Therefore, diamond cannot conduct electricity and is not suitable for use as an anode.

6. **Conclusion**:
- The assertion that graphite is used as an anode while diamond is not is correct because graphite has free electrons that allow it to conduct electricity, whereas diamond does not have free electrons due to its bonding structure.

7. **Final Answer**:
- The assertion is correct, and the reason provided (the existence of free electrons in graphite) is also correct and explains why graphite is used as an anode.