An alkane containing atleast _____ carbon atoms is converted into an aromatic hydrocarbon, when heated in presence of `Cr_(2)O_(3)` on `Al_(2)O_(3)`.

Options

A. 6
B. 4
C. 3
D. 5

Answer

To determine the minimum number of carbon atoms in an alkane that can be converted into an aromatic hydrocarbon when heated in the presence of `Cr_(2)O_(3)` on `Al_(2)O_(3)`, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Reaction**: The question involves the conversion of an alkane to an aromatic hydrocarbon. Aromatic hydrocarbons are characterized by having a cyclic structure with sp² hybridized carbon atoms.

2. **Identifying the Alkane**: The alkane that is commonly referenced in this type of reaction is cyclohexane. Cyclohexane (C₆H₁₂) is a saturated hydrocarbon (alkane) that contains 6 carbon atoms.

3. **Reaction Conditions**: When cyclohexane is heated in the presence of `Cr_(2)O_(3)` on `Al_(2)O_(3)`, it undergoes a dehydrogenation reaction to form benzene (C₆H₆) and hydrogen gas (H₂). The balanced reaction can be written as:
\[ C_6H_{12} \xrightarrow{Cr_2O_3/Al_2O_3} C_6H_6 + 3H_2 \]

4. **Aromatic Hydrocarbon Formation**: Benzene is the simplest aromatic hydrocarbon, and it has 6 carbon atoms. For an alkane to be converted into benzene, it must contain at least 6 carbon atoms.

5. **Conclusion**: Therefore, the minimum number of carbon atoms in the alkane that can be converted into an aromatic hydrocarbon (specifically benzene) is 6.

### Final Answer:
An alkane containing at least **6 carbon atoms** is converted into an aromatic hydrocarbon when heated in the presence of `Cr_(2)O_(3)` on `Al_(2)O_(3)`.