Which of the following molecules has the maximum bond enthalpy?

Options

A. `N_2(g)`
B. `CO(g)`
C. `F_2(g)`
D. `HF(g)`

Explanation

To determine which of the following molecules has the maximum bond enthalpy, we will analyze the bond order and the nature of the bonds in each molecule. The molecules in question are nitrogen gas (N₂), carbon monoxide (CO), fluorine gas (F₂), and hydrofluoric acid (HF).

### Step-by-Step Solution:

1. **Identify the Bond Types and Structures**:
- **Nitrogen (N₂)**: Contains a triple bond (N≡N) between two nitrogen atoms. Each nitrogen atom has one lone pair.
- **Carbon Monoxide (CO)**: Contains a triple bond (C≡O) between carbon and oxygen. Carbon has one lone pair, and oxygen has two lone pairs.
- **Fluorine (F₂)**: Contains a single bond (F-F) between two fluorine atoms. Each fluorine atom has three lone pairs.
- **Hydrofluoric Acid (HF)**: Contains a single bond (H-F) between hydrogen and fluorine. Fluorine has three lone pairs, and hydrogen has no lone pairs.

2. **Determine the Bond Order**:
- **N₂**: Bond order = 3 (triple bond)
- **CO**: Bond order = 3 (triple bond)
- **F₂**: Bond order = 1 (single bond)
- **HF**: Bond order = 1 (single bond)

3. **Analyze Bond Strength**:
- The bond enthalpy is directly related to the bond order: higher bond order generally means stronger bonds.
- Both N₂ and CO have a bond order of 3, indicating they have strong bonds.

4. **Consider Polarity and Resonance**:
- **N₂** is a non-polar molecule.
- **CO** is a polar molecule because oxygen is more electronegative than carbon, which can lead to additional stabilization.
- The presence of resonance in CO can also contribute to its bond strength.

5. **Compare Bond Enthalpies**:
- While both N₂ and CO have the same bond order, the bond enthalpy of CO is higher due to its polarity and resonance effects.
- F₂ and HF have much lower bond enthalpies due to their single bonds.

6. **Conclusion**:
- Therefore, the molecule with the maximum bond enthalpy among the given options is **Carbon Monoxide (CO)**.

### Final Answer:
**Carbon Monoxide (CO)** has the maximum bond enthalpy.