A: Alkene `A(Me_2 C = CMe_2)` is more stable than alkene `B(Et_2 C = Cet_2)`
R: Baker-Nathan effect.

Options

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

Explanation

To solve the question regarding the stability of alkenes A and B, we will analyze the structures and apply the concept of hyperconjugation, also known as the Baker-Nathan effect.

### Step-by-Step Solution:

1. **Identify the Structures of Alkenes A and B**:
- Alkene A: \( \text{Me}_2C = C\text{Me}_2 \) (2,3-dimethylbutene)
- Alkene B: \( \text{Et}_2C = C\text{Et}_2 \) (2,3-diethylbutene)

2. **Draw the Structures**:
- Alkene A has two methyl groups attached to each carbon of the double bond.
- Alkene B has two ethyl groups attached to each carbon of the double bond.

3. **Count the Alpha Hydrogens**:
- Alpha hydrogens are the hydrogens attached to the carbons adjacent to the double bond.
- For Alkene A:
- Each carbon in the double bond has 6 alpha hydrogens (3 from each methyl group).
- Total alpha hydrogens in A = 12.
- For Alkene B:
- Each carbon in the double bond has 4 alpha hydrogens (2 from each ethyl group).
- Total alpha hydrogens in B = 8.

4. **Analyze Hyperconjugation**:
- Hyperconjugation refers to the stabilizing interaction that results from the overlap of a sigma bond orbital with an empty p-orbital or a pi-bond orbital.
- The more alpha hydrogens present, the greater the hyperconjugation effect, leading to increased stability of the alkene.

5. **Compare Stability**:
- Alkene A has more alpha hydrogens (12) compared to Alkene B (8).
- Therefore, Alkene A is more stable due to a greater extent of hyperconjugation.

6. **Conclusion**:
- The assertion (A is more stable than B) is true.
- The reason (Baker-Nathan effect) is also true and explains why A is more stable than B.

### Final Answer:
Both the assertion and reason are true, and the reason is the correct explanation for the assertion.