Which of the following `IUPAC` name is incorrect?
(i) `2`-Methyl-`3`-ethylpentane
(ii) `2`-Ethyl-`3`-methylpentane
(iii) `3`-Methyl-`2`-ethylpentane
(iv) `3`-Ethyl-`2`-methylpentane.

Options

A. (i), (ii),(iii), (iv)
B. (ii), (iii), (iv)
C. (i), (ii), (iii)
D. (i), (iv)

Explanation

To determine which of the given IUPAC names is incorrect, we will analyze each option step by step based on the rules of IUPAC nomenclature.

### Step 1: Analyze Option (i) `2-Methyl-3-ethylpentane`
1. Identify the longest carbon chain: The base name is "pentane," which indicates a five-carbon chain.
2. Identify substituents: There is a methyl group on carbon 2 and an ethyl group on carbon 3.
3. Check alphabetical order: According to IUPAC rules, substituents should be listed in alphabetical order. Ethyl (E) comes before methyl (M).
4. Conclusion: The correct name should be `2-Ethyl-3-methylpentane`. Therefore, this option is incorrect.

### Step 2: Analyze Option (ii) `2-Ethyl-3-methylpentane`
1. Identify the longest carbon chain: The base name is "pentane," indicating a five-carbon chain.
2. Identify substituents: There is an ethyl group on carbon 2 and a methyl group on carbon 3.
3. Check alphabetical order: The name follows the correct alphabetical order (E before M).
4. Conclusion: This option is correct.

### Step 3: Analyze Option (iii) `3-Methyl-2-ethylpentane`
1. Identify the longest carbon chain: The base name is "pentane," indicating a five-carbon chain.
2. Identify substituents: There is a methyl group on carbon 3 and an ethyl group on carbon 2.
3. Check alphabetical order: The name does not follow the correct alphabetical order (E should come before M).
4. Conclusion: The correct name should be `2-Ethyl-3-methylpentane`. Therefore, this option is incorrect.

### Step 4: Analyze Option (iv) `3-Ethyl-2-methylpentane`
1. Identify the longest carbon chain: The base name is "pentane," indicating a five-carbon chain.
2. Identify substituents: There is an ethyl group on carbon 3 and a methyl group on carbon 2.
3. Check alphabetical order: The name does not follow the correct alphabetical order (E should come before M).
4. Conclusion: The correct name should be `2-Ethyl-3-methylpentane`. Therefore, this option is incorrect.

### Final Conclusion:
The incorrect IUPAC names are:
- Option (i) `2-Methyl-3-ethylpentane`
- Option (iii) `3-Methyl-2-ethylpentane`
- Option (iv) `3-Ethyl-2-methylpentane`