Which of the following formulae represent an alkane?

Options

A. `C_10H_20`
B. `C_7H_16`
C. `C_5H_8`
D. `C_9H_10`

Answer

To determine which of the given formulae represents an alkane, we need to understand the general formula for alkanes and how they differ from alkenes and alkynes.

### Step-by-Step Solution:

1. **Understand the General Formula for Alkanes**:
- Alkanes are saturated hydrocarbons and follow the general formula:
\[ C_nH_{2n+2} \]
- Here, \( n \) is the number of carbon atoms in the molecule.

2. **Identify the General Formulas for Other Hydrocarbons**:
- Alkenes (unsaturated hydrocarbons) follow the formula:
\[ C_nH_{2n} \]
- Alkynes (also unsaturated) follow the formula:
\[ C_nH_{2n-2} \]

3. **Evaluate Given Formulae**:
- We need to check each provided formula against the alkane formula \( C_nH_{2n+2} \).
- For example, if we have a formula like \( C_7H_{16} \):
- Here, \( n = 7 \).
- Plugging into the alkane formula:
\[ C_7H_{2(7)+2} = C_7H_{14+2} = C_7H_{16} \]
- This matches the alkane formula.

4. **Check Other Options**:
- If we have \( C_{10}H_{20} \):
- Here, \( n = 10 \).
- Plugging into the alkane formula:
\[ C_{10}H_{2(10)+2} = C_{10}H_{20+2} = C_{10}H_{22} \]
- This does not match, indicating it could be an alkene.
- If we have \( C_5H_8 \):
- Here, \( n = 5 \).
- Plugging into the alkane formula:
\[ C_5H_{2(5)+2} = C_5H_{10+2} = C_5H_{12} \]
- This does not match either, indicating it could be an alkyne.

5. **Conclusion**:
- After checking the formulae, we find that \( C_7H_{16} \) is the only formula that fits the alkane structure \( C_nH_{2n+2} \).

### Final Answer:
The formula that represents an alkane is \( C_7H_{16} \).