A : When `C_(2) H_(5) - O- CH_(3)` is reacted with one mole of Hl then `C_(2)H_(5)OH` & `CH_(3) I` is formed .
R : It is `S_(N)1` reaction

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 question step by step, let's analyze the assertion and reason provided:

### Step 1: Analyze the Assertion
The assertion states that when \( C_2H_5OCH_3 \) (ethyl methyl ether) is reacted with one mole of HI (hydroiodic acid), the products formed are \( C_2H_5OH \) (ethanol) and \( CH_3I \) (methyl iodide).

1. **Reaction Mechanism**:
- The ether \( C_2H_5OCH_3 \) reacts with HI. The oxygen in the ether has lone pairs that can protonate by the hydrogen ion (H⁺) from HI.
- This leads to the formation of a protonated ether, which is more reactive.

2. **Cleavage of Ether**:
- The protonated ether will undergo cleavage, leading to the formation of \( C_2H_5OH \) and \( CH_3I \).
- The reaction can be summarized as:
\[ C_2H_5OCH_3 + HI \rightarrow C_2H_5OH + CH_3I \]

Thus, the assertion is **true**.

### Step 2: Analyze the Reason
The reason states that the reaction is an \( S_N1 \) reaction.

1. **Understanding \( S_N1 \) Mechanism**:
- An \( S_N1 \) reaction involves the formation of a carbocation intermediate. It typically occurs with tertiary or some secondary substrates where the carbocation is stable.
- In this case, the ether does not form a stable carbocation; instead, it undergoes a bimolecular nucleophilic substitution.

2. **Actual Mechanism**:
- The reaction proceeds via an \( S_N2 \) mechanism, where the nucleophile (I⁻) attacks the less hindered carbon atom directly, leading to the formation of products in a single step without forming a stable carbocation.

Thus, the reason is **false**.

### Conclusion
- The assertion is true, and the reason is false. Therefore, the correct option is:
**Assertion True, Reason False** (Option 3).