The correct `IUPAC` name of `2-`ethyl`-3-`pentyne is

Options

A. `3-`methyl hexyne `-4`
B. `4-`ethyl pentyne `-2`
C. `4-`methyl hex `-2-`yne
D. None of these

Explanation

To determine the correct IUPAC name for the compound originally referred to as "2-ethyl-3-pentyne," we will follow these steps:

### Step-by-Step Solution:

1. **Identify the Base Chain**:
- The name "pentyne" suggests that the longest continuous carbon chain has 5 carbon atoms and contains a triple bond. However, we need to check if there is a longer chain available.
- The base name "pent" indicates a 5-carbon chain, but we will examine the structure to see if a longer chain exists.

2. **Draw the Structure**:
- Start by drawing a 5-carbon chain (pentane) and place a triple bond on the 3rd carbon as indicated by "3-pentyne."
- Next, add an ethyl group (C2H5) on the 2nd carbon of the pentane chain.

3. **Count the Carbons**:
- After drawing the structure, count the total number of carbon atoms in the longest chain.
- In this case, you will find that there are actually 6 carbon atoms when you include the ethyl group.

4. **Identify the Longest Chain**:
- The longest continuous chain should be selected for naming. In this case, the longest chain is 6 carbons (hexane) instead of the original 5 (pentane).
- Number the longest chain starting from the end closest to the triple bond.

5. **Determine Substituents and Their Positions**:
- With the longest chain identified as hexane, we now have a substituent (ethyl) that is on the 4th carbon.
- The triple bond is now located on the 2nd carbon of this 6-carbon chain.

6. **Construct the IUPAC Name**:
- The IUPAC name is constructed by combining the substituent name and its position with the base name and the position of the triple bond.
- The final name will be "4-ethyl-2-heptyne" (since there are 7 carbons in total, not 6).

### Final Answer:
The correct IUPAC name of the compound is **4-ethyl-2-heptyne**.