Valence-bond theory is one of the two quantum mechanical approaches that explains bonding in molecules In some cases, valence bond theroy cannot cannot satisfactorily account for observed properties of molecules
Bond order and magnetic behaviour shown by different species have been matched Which is the incorrect matching .

Options

A. `{:("Species",,"Bond order",,"Magentic behaviour"),(CN^(Θ)(14),,3.0,,"dimagnetic"):}`
B. `{:("Species",,"Bond order",,"Magentic behaviour"),(BN(14),,2.0,,"dimagnetic"):}`
C. `{:("Species",,"Bond order",,"Magentic behaviour"),(C_(2)(12),,2.0,,"dimagnetic"):}`
D. `{:("Species",,"Bond order",,"Magentic behaviour"),(B_(2)(10),,3.0,,"paramagnetic"):}`

Explanation

To solve the question regarding the incorrect matching of bond order and magnetic behavior of different species, we will analyze each species step by step.

### Step 1: Analyze CN⁻
1. **Determine the total number of electrons**:
- Carbon (C) has 6 electrons, Nitrogen (N) has 7 electrons. The negative charge adds 1 electron.
- Total = 6 + 7 + 1 = 14 electrons.

2. **Fill the molecular orbitals**:
- Molecular orbital filling order: σ1s, σ*1s, σ2s, σ*2s, π2p_x, π2p_y, σ2p_z.
- Fill the 14 electrons:
- σ1s (2), σ*1s (2), σ2s (2), σ*2s (2), π2p_x (2), π2p_y (2), σ2p_z (2).
- Bonding electrons = 10, Anti-bonding electrons = 4.

3. **Calculate bond order**:
- Bond order = 1/2 * (Bonding electrons - Anti-bonding electrons) = 1/2 * (10 - 4) = 3.

4. **Determine magnetic behavior**:
- All electrons are paired, so CN⁻ is diamagnetic.

### Step 2: Analyze BN
1. **Determine the total number of electrons**:
- Boron (B) has 5 electrons, Nitrogen (N) has 7 electrons.
- Total = 5 + 7 = 12 electrons.

2. **Fill the molecular orbitals**:
- Fill the 12 electrons:
- σ1s (2), σ*1s (2), σ2s (2), σ*2s (2), π2p_x (2), π2p_y (2).
- Bonding electrons = 8, Anti-bonding electrons = 4.

3. **Calculate bond order**:
- Bond order = 1/2 * (8 - 4) = 2.

4. **Determine magnetic behavior**:
- All electrons are paired, so BN is diamagnetic.

### Step 3: Analyze C₂
1. **Determine the total number of electrons**:
- Each Carbon (C) has 6 electrons, so for 2 Carbons:
- Total = 6 + 6 = 12 electrons.

2. **Fill the molecular orbitals**:
- Fill the 12 electrons:
- σ1s (2), σ*1s (2), σ2s (2), σ*2s (2), π2p_x (2), π2p_y (2).
- Bonding electrons = 8, Anti-bonding electrons = 4.

3. **Calculate bond order**:
- Bond order = 1/2 * (8 - 4) = 2.

4. **Determine magnetic behavior**:
- All electrons are paired, so C₂ is diamagnetic.

### Step 4: Analyze B₂
1. **Determine the total number of electrons**:
- Each Boron (B) has 5 electrons, so for 2 Borons:
- Total = 5 + 5 = 10 electrons.

2. **Fill the molecular orbitals**:
- Fill the 10 electrons:
- σ1s (2), σ*1s (2), σ2s (2), σ*2s (2), π2p_x (2), π2p_y (0).
- Bonding electrons = 6, Anti-bonding electrons = 4.

3. **Calculate bond order**:
- Bond order = 1/2 * (6 - 4) = 1.

4. **Determine magnetic behavior**:
- There are unpaired electrons, so B₂ is paramagnetic.

### Conclusion
Now we can summarize the findings:

- **CN⁻**: Bond order = 3, Diamagnetic (Correct)
- **BN**: Bond order = 2, Diamagnetic (Correct)
- **C₂**: Bond order = 2, Diamagnetic (Correct)
- **B₂**: Bond order = 1, Paramagnetic (Correct)

### Incorrect Matching
The incorrect matching is for **BN** since it was initially stated to have 14 electrons (which is incorrect).

### Final Answer
The incorrect matching is for **BN**.