(A) Rate of nitration of benzene and hexadeuterobenzene are different.
(R) C-H bond is stronger than C-D bond.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion
B. If both assertion and reason are true but reason is not the correct explanation of assertion
C. If assertion is true but reason is false
D. If both assertion and reason are false

Explanation

To solve the given assertion and reason question, we will analyze both statements step by step.

### Step 1: Analyze the Assertion
The assertion states that "the rate of nitration of benzene and hexadeuterobenzene are different."

- **Understanding Nitration**: Nitration of benzene involves the electrophilic substitution reaction where a nitro group (NO2) replaces a hydrogen atom on the benzene ring. The rate of this reaction depends on the stability of the intermediate carbocation formed during the reaction, which is influenced by the nature of the substituents on the benzene ring.
- **Benzene vs. Hexadeuterobenzene**: Hexadeuterobenzene (C6D6) is a deuterated form of benzene where all hydrogen atoms are replaced by deuterium (D). The rate of nitration is primarily influenced by the availability of the electrophile rather than the specific isotopes present in the molecule.

**Conclusion for Assertion**: The assertion is **false** because the rate of nitration does not significantly differ between benzene and hexadeuterobenzene.

### Step 2: Analyze the Reason
The reason states that "C-H bond is stronger than C-D bond."

- **Bond Strength Comparison**: The C-H bond (carbon-hydrogen) and C-D bond (carbon-deuterium) can be compared based on their bond dissociation energies. Deuterium is an isotope of hydrogen with a greater mass, which affects the bond strength.
- **Vibrational Energy**: The C-D bond is generally stronger than the C-H bond because the increased mass of deuterium leads to lower vibrational energy levels. This means that more energy is required to break the C-D bond compared to the C-H bond.

**Conclusion for Reason**: The reason is also **false** because the C-D bond is stronger than the C-H bond.

### Final Conclusion
Both the assertion and the reason are false. Therefore, the correct answer is that both statements are incorrect.