Which of the following molecules has the longest nitrogen-nitrogen bond?

Options

A. `N_2H_4`
B. `N_2`
C. `N_2F_2`
D. All have equal bond lengths

Explanation

To determine which molecule has the longest nitrogen-nitrogen (N-N) bond, we need to analyze the bond types present in the given molecules. The bond length is influenced by the bond order, which is the number of bonds between two atoms. Generally, single bonds are longer than double bonds, and double bonds are longer than triple bonds.

### Step-by-Step Solution:

1. **Identify the Molecules**: First, we need to identify the molecules in question. Common nitrogen-containing molecules include hydrazine (N2H4), nitrogen gas (N2), and others like azide (N3^-), etc.

2. **Draw the Lewis Structures**: For each molecule, we will draw the Lewis structure to visualize the bonding:
- **N2 (Nitrogen gas)**: This molecule has a triple bond between the two nitrogen atoms.
- **N2H4 (Hydrazine)**: In this molecule, there are two nitrogen atoms bonded by a single bond, and each nitrogen is also bonded to two hydrogen atoms.
- **Other Molecules**: If there are other options, we would need to analyze their structures similarly.

3. **Determine Bond Types**:
- **N2**: Triple bond (N≡N)
- **N2H4**: Single bond (N-N)
- **Other Molecules**: Analyze their bond types.

4. **Compare Bond Lengths**:
- A triple bond (N≡N) is shorter than a double bond (N=N), which is shorter than a single bond (N-N).
- Therefore, among the molecules analyzed, the single bond in N2H4 will be longer than the triple bond in N2.

5. **Conclusion**: Based on the bond types, the molecule with the longest nitrogen-nitrogen bond is **N2H4 (hydrazine)**, as it contains a single bond between the nitrogen atoms.

### Final Answer:
The molecule with the longest nitrogen-nitrogen bond is **N2H4 (hydrazine)**.