The iso-octane is:

Question

The iso-octane is:

Accepted Answer

The iso-octane is correctly identified as 2,2,4-trimethyl pentane, which is Option 3. Here's a detailed explanation supporting this:

1. **Explanation for Option 3 (2,2,4-trimethyl pentane):**
   - Iso-octane is a common name for 2,2,4-trimethyl pentane. It is a branched-chain alkane with the molecular formula C8H18. The structure consists of a five-carbon chain (pentane) with three methyl groups attached at the 2nd and 4th carbon atoms. This specific arrangement of carbon atoms gives iso-octane its characteristic properties, such as high resistance to knocking in internal combustion engines, which is why it is used as a standard reference fuel with an octane rating of 100.

2. **Explanation for why other options are incorrect:**

- **Option 1 (3-methyl heptane):**
     - 3-methyl heptane is a different isomer of octane. It consists of a seven-carbon chain (heptane) with a single methyl group attached to the third carbon. This structure does not match the branched structure of iso-octane and does not have the same anti-knock properties.

- **Option 2 (2,4-dimethyl hexane):**
     - 2,4-dimethyl hexane is another isomer of octane, with a six-carbon chain (hexane) and two methyl groups attached at the 2nd and 4th carbon atoms. While it is a branched alkane, it does not have the specific branching pattern of 2,2,4-trimethyl pentane, and thus, it is not iso-octane.

- **Option 4 (4-methyl heptane):**
     - 4-methyl heptane is also an isomer of octane, featuring a seven-carbon chain with a single methyl group attached to the fourth carbon. Like the other incorrect options, its structure does not match that of iso-octane, and it lacks the same performance characteristics in engines.

In conclusion, Option 3, 2,2,4-trimethyl pentane, is the correct answer because it accurately represents the chemical structure known as iso-octane, which is used as a standard for measuring octane ratings in fuels.