Assertion (A) IUPAC name of the compound
`CH_(3)-underset(CH_(3))underset(|)(CH)-O-CH_(2)-CH_(2)-CH_(3)` is 2-ethoxy-2-methylethane
Reason (R) In IUPAC nonmenclature, ether is regarded as hydrocarbon derivative in which a hydrogen atom is replaced by -OR and or -OAr group [where, R = alkyl group and Ar = aryl group].

Options

A. Assertion and reason both are correct and reason is correct explanation of assertion.
B. Assertion and reason both are wrong statements.
C. Assertion is correct statement but reason is wrong statement.
D. Assertion is wrong statement but reason is correct statement.

Explanation

To solve the question, we need to analyze the assertion and reason provided regarding the IUPAC naming of the compound and the definition of ethers.

### Step-by-Step Solution:

1. **Identify the Structure**: The given compound is CH₃-CH(CH₃)-O-CH₂-CH₂-CH₃. This indicates that there is an ether functional group (O) connecting two alkyl groups.

2. **Determine the Alkyl Groups**:
- On the left side of the ether oxygen (O), we have a carbon chain with a methyl group (CH₃) attached to the second carbon. This gives us a 2-methyl group on a 2-carbon chain (ethane).
- On the right side of the ether oxygen, we have a straight chain of 3 carbons (CH₂-CH₂-CH₃), which is a propyl group.

3. **Number the Carbon Chain**:
- We start numbering from the end of the chain closest to the ether oxygen. This gives us:
- 1: CH₃ (methyl)
- 2: CH (with a methyl group)
- 3: O
- 4: CH₂
- 5: CH₂
- 6: CH₃ (propyl)

4. **Naming the Ether**:
- In IUPAC nomenclature, ethers are named by identifying the two alkyl groups attached to the oxygen. The larger alkyl group is usually named first.
- Here, we have a propyl group and a 2-methyl group attached to the ether oxygen.

5. **Construct the Name**:
- The correct IUPAC name for this compound is 1-methoxy-2-methylpropane, not 2-ethoxy-2-methylethane as stated in the assertion.

6. **Evaluate the Assertion and Reason**:
- **Assertion (A)**: The assertion states that the IUPAC name is 2-ethoxy-2-methylethane, which is incorrect.
- **Reason (R)**: The reason correctly describes the nomenclature of ethers, stating that ethers are hydrocarbon derivatives where a hydrogen atom is replaced by an -OR or -OAr group.

7. **Conclusion**: Since the assertion is incorrect and the reason is correct, the final answer is that the assertion is false, but the reason is true.

### Final Answer:
- Assertion (A) is incorrect.
- Reason (R) is correct.
- Therefore, the correct option is D.