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 both the assertion (A) and the reason (R) provided regarding the IUPAC naming of the compound and the principles of ether nomenclature.

### Step 1: Analyze the Structure
The compound given is `CH3-CH(CH3)-O-CH2-CH2-CH3`. We need to identify the longest carbon chain and the substituents.

### Step 2: Identify the Longest Carbon Chain
In the structure, the longest continuous carbon chain is a 3-carbon chain (propane) connected to an ether group. The ether group is `-O-` and is connected to a propyl group (`CH2-CH2-CH3`).

### Step 3: Identify the Substituents
The substituents on the main chain include:
- A methoxy group (`-O-CH3`) attached to the second carbon.
- A propoxy group (`-O-CH2-CH2-CH3`) also attached to the second carbon.

### Step 4: Naming the Compound
According to IUPAC nomenclature:
- The main chain is propane (3 carbons).
- The substituents are identified as propoxy and methoxy.
- The correct name for the compound would be 2-methoxy-2-propoxypropane.

### Step 5: Evaluate the Assertion
The assertion states that the IUPAC name is 2-ethoxy-2-methylethane. This is incorrect because the correct name is 2-methoxy-2-propoxypropane, as derived in the previous step.

### Step 6: Evaluate the Reason
The reason states that in IUPAC nomenclature, ether is regarded as a hydrocarbon derivative in which a hydrogen atom is replaced by an -OR or -OAr group. This statement is correct as it accurately describes the nomenclature of ethers.

### Conclusion
- The assertion (A) is **incorrect**.
- The reason (R) is **correct**.

Thus, the answer is that the assertion is false while the reason is true.

### Final Answer
Assertion (A) is incorrect, and Reason (R) is correct.