A : `CH_(3)-underset(CH_(3))underset(|)overset(CH_(3))overset(|)(C)-O-CH_(3)` on reaction with conc. Hl gives ` CH_(3) - underset(CH_(3))underset(|)overset(CH_(3))overset(|)(C)-I and CH_(3)OH` major product .
R : This reaction proceed by `S_(N)1` mechanism .

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark (1)
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark (2)
C. If Assertion is true statement but Reason is false , then mark (3)
D. If both Assertion and Reason are false statements , then mark (4)

Answer

To solve the given question, we need to analyze the assertion and reason provided, and verify their correctness step by step.

### Step 1: Analyze the Assertion
The assertion states that the compound `CH3-C(CH3)2-O-CH3` reacts with concentrated HI to give `CH3-C(CH3)2-I` and `CH3OH` as major products.

1. **Identify the Reactant**: The reactant is an ether, specifically a methoxy derivative of a tert-butyl structure.
2. **Reaction with HI**: When this ether reacts with concentrated HI, the ether bond (C-O) is cleaved. The oxygen atom in the ether can be protonated by HI, making it a better leaving group.
3. **Formation of Products**: The cleavage of the ether bond leads to the formation of a tertiary carbocation and methanol (CH3OH). The iodide ion (I-) from HI can then attack the carbocation to form the iodo compound.

**Conclusion for Assertion**: The assertion is true as the reaction does produce the stated major products.

### Step 2: Analyze the Reason
The reason states that the reaction proceeds by an SN1 mechanism.

1. **Understanding SN1 Mechanism**: The SN1 mechanism involves two steps:
- Formation of a carbocation (rate-determining step).
- Nucleophilic attack by the iodide ion on the carbocation.
2. **Stability of Carbocation**: In this case, the formation of a tertiary carbocation is favored due to its stability, which supports the SN1 pathway.
3. **Product Formation**: The nucleophile (I-) attacks the carbocation leading to the formation of the iodo compound.

**Conclusion for Reason**: The reason is also true, as it correctly describes the mechanism of the reaction.

### Final Conclusion
Both the assertion and the reason are true, and the reason correctly explains the assertion. Therefore, the correct option is:

**Option 1**: Both assertion and reason are true, and reason is the correct explanation of the assertion.