The following reaction takes place through `CH_3-O-CH_2-CH_3 + HI` to `CH_3-I + CH_3-CH_2-OH`

Options

A. `S_N1` mechanism
B. `S_N2` mechanism
C. `S_N1` in first step and E2 in second step
D. `S_N2` in first step and E1 in second step

Answer

To determine the mechanism of the reaction between CH₃-O-CH₂-CH₃ (ethyl methyl ether) and HI (hydroiodic acid) to form CH₃-I (methyl iodide) and CH₃-CH₂-OH (ethanol), we will analyze the steps involved in the reaction.

### Step-by-Step Solution:

1. **Identify the Reactants and Products:**
- Reactants: CH₃-O-CH₂-CH₃ + HI
- Products: CH₃-I + CH₃-CH₂-OH

2. **Protonation of the Ether:**
- The ether (CH₃-O-CH₂-CH₃) reacts with HI. The oxygen atom in the ether has lone pairs and can donate one of these lone pairs to the hydrogen ion (H⁺) from HI, resulting in the protonation of the ether.
- This leads to the formation of a protonated ether (CH₃-O⁺-CH₂-CH₃).

3. **Formation of the Leaving Group:**
- The protonated ether is now more reactive. The bond between the oxygen and the CH₂ group becomes weaker due to the positive charge on the oxygen. This allows the CH₂ group to leave as a carbocation (CH₃-O⁺-CH₂⁺) and I⁻ (iodide ion) to be released.

4. **Nucleophilic Attack:**
- The iodide ion (I⁻), which is a good nucleophile, can now attack the carbocation formed in the previous step. This attack occurs at the carbon atom that was previously bonded to the leaving group (CH₂).
- The nucleophilic attack by I⁻ results in the formation of CH₃-I (methyl iodide).

5. **Formation of Ethanol:**
- The remaining part of the ether (CH₃-CH₂-OH) is formed as a byproduct when the ether is cleaved.

6. **Determine the Mechanism:**
- The reaction involves the formation of a carbocation intermediate and a nucleophilic attack by I⁻, which indicates that the mechanism is bimolecular nucleophilic substitution (SN2). The nucleophile attacks the substrate in a single step, leading to the formation of products.

### Conclusion:
The mechanism for the reaction of CH₃-O-CH₂-CH₃ with HI to form CH₃-I and CH₃-CH₂-OH is an **SN2 mechanism**.