Which of the following gas has the highest heat of combustion ?

Options

A. Methane
B. Ethane
C. Ethene
D. Ethyne

Explanation

To determine which gas has the highest heat of combustion, we need to analyze the number of sigma bonds present in each gas. The heat of combustion is directly related to the number of sigma bonds; more sigma bonds generally mean a higher heat of combustion.

### Step-by-Step Solution:

1. **Identify the Gases**: We need to analyze the following gases:
- Methane (CH₄)
- Ethane (C₂H₆)
- Ethylene (C₂H₄)
- Acetylene (C₂H₂)

2. **Draw the Structures and Count Sigma Bonds**:
- **Methane (CH₄)**:
- Structure: H
|
C - H
|
H
|
H
- Number of sigma bonds: 4 (C-H bonds)

- **Ethane (C₂H₆)**:
- Structure: H H
| |
C - C
| |
H H
- Number of sigma bonds: 7 (6 C-H bonds + 1 C-C bond)

- **Ethylene (C₂H₄)**:
- Structure: H H
| |
C = C
| |
H H
- Number of sigma bonds: 5 (4 C-H bonds + 1 C-C bond)

- **Acetylene (C₂H₂)**:
- Structure: H - C ≡ C - H
- Number of sigma bonds: 3 (2 C-H bonds + 1 C-C bond)

3. **Compare the Number of Sigma Bonds**:
- Methane (CH₄): 4 sigma bonds
- Ethane (C₂H₆): 7 sigma bonds
- Ethylene (C₂H₄): 5 sigma bonds
- Acetylene (C₂H₂): 3 sigma bonds

4. **Determine the Gas with the Highest Heat of Combustion**:
- Since ethane has the highest number of sigma bonds (7), it will have the highest heat of combustion.

### Conclusion:
The gas with the highest heat of combustion is **Ethane (C₂H₆)**.

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