Assertion (A) : `Ph overset (o+)(N_2) Br^(Θ)` couples with `N, N`-dimethyl aniline (I) but not with ` 2,6,`-dimethyl-`N,N`-dimethuyl aniline (II)
Reason (R ): Due to steric inhibition of resonance , the p-position of (II) is not sufficiently activated fro the coupling reaction.

Options

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

Explanation

To solve the problem, we need to analyze the assertion and reason provided in the question regarding the coupling of diazonium salts with two different anilines.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that the compound `Ph-(o+)(N2)Br^Θ` couples with `N,N`-dimethyl aniline (I) but does not couple with `2,6`-dimethyl `N,N`-dimethyl aniline (II).
- Here, `Ph` represents a phenyl group, and `N2` indicates a diazonium group. The coupling reaction involves the formation of a new bond between the diazonium salt and the aniline.

2. **Analyzing Compound I (N,N-dimethyl aniline)**:
- In the case of `N,N`-dimethyl aniline, the nitrogen atom has two methyl groups and a lone pair.
- The lone pair on the nitrogen can participate in resonance with the benzene ring, enhancing the nucleophilicity of the para position.
- This allows the para position of the benzene ring to be activated, facilitating the coupling reaction with the diazonium salt.

3. **Analyzing Compound II (2,6-dimethyl-N,N-dimethyl aniline)**:
- For `2,6`-dimethyl `N,N`-dimethyl aniline, the two methyl groups are positioned ortho to the amino group.
- These bulky methyl groups create steric hindrance, which affects the ability of the lone pair on the nitrogen to participate in resonance with the benzene ring.
- The steric hindrance causes the nitrogen's lone pair to be less available for resonance, leading to a situation where the para position is not sufficiently activated for the coupling reaction.

4. **Understanding the Reason (R)**:
- The reason states that due to steric inhibition of resonance, the para position of compound II is not sufficiently activated for the coupling reaction.
- This is a correct explanation for why the coupling does not occur with compound II, as the steric hindrance prevents effective overlap between the lone pair on nitrogen and the π system of the benzene ring.

5. **Conclusion**:
- Both the assertion and the reason are true, and the reason correctly explains the assertion. Thus, the answer is that both statements are correct.

### Final Answer:
Both Assertion (A) and Reason (R) are true, and R is the correct explanation of A.

---