What is the minimum number of carbon atoms of an alkane must have to form an isomer?

Options

A. 4
B. 3
C. 2
D. 1

Answer

To determine the minimum number of carbon atoms an alkane must have to form an isomer, we can analyze the structure of alkanes and their potential for isomerism.

### Step-by-Step Solution:

1. **Understanding Alkanes**: Alkanes are saturated hydrocarbons with the general formula CnH2n+2. They consist only of carbon (C) and hydrogen (H) atoms.

2. **Identifying the Smallest Alkane**: The smallest alkane is methane (CH4), which has one carbon atom. Methane cannot form any isomers because there are no alternative arrangements of carbon and hydrogen atoms.

3. **Moving to Larger Alkanes**: The next alkane is ethane (C2H6), which has two carbon atoms. Ethane also cannot form isomers since there is only one way to arrange two carbon atoms with the corresponding hydrogen atoms.

4. **Considering Propane**: The next alkane is propane (C3H8), which has three carbon atoms. Similar to ethane, propane cannot form isomers because there is only one linear arrangement of three carbon atoms.

5. **Analyzing Butane**: When we reach butane (C4H10), which has four carbon atoms, we can start to see the possibility of isomerism. Butane can exist in two different structural forms:
- n-butane (a straight chain of four carbon atoms)
- isobutane (a branched chain with three carbon atoms in a row and one carbon as a side chain)

6. **Conclusion**: Therefore, the minimum number of carbon atoms required for an alkane to form isomers is **four**.

### Final Answer:
The minimum number of carbon atoms an alkane must have to form an isomer is **4**.

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