To determine which of the following species is not paramagnetic, we need to analyze the electronic configurations of each species and check for the presence of unpaired electrons. A species is paramagnetic if it has unpaired electrons, while it is diamagnetic (not paramagnetic) if all its electrons are paired.
Let's analyze each species step by step:
### Step 1: Analyze CO (Carbon Monoxide)
1. **Count the total number of electrons**:
- Carbon (C) has 6 electrons, and Oxygen (O) has 8 electrons.
- Total = 6 + 8 = 14 electrons.
2. **Write the molecular orbital configuration**:
- The order of filling the molecular orbitals is:
- σ1s², σ*1s², σ2s², σ*2s², σ2p_z², π2p_x², π2p_y².
- Filling the orbitals:
- σ1s² (2), σ*1s² (2), σ2s² (2), σ*2s² (2), σ2p_z² (2), π2p_x² (2), π2p_y² (2).
- Total = 2 + 2 + 2 + 2 + 2 + 2 + 2 = 14 electrons.
3. **Check for unpaired electrons**:
- All electrons are paired in CO.
- Therefore, CO is **diamagnetic** (not paramagnetic).
### Step 2: Analyze O2 (Oxygen)
1. **Count the total number of electrons**:
- Oxygen has 8 electrons, so for O2:
- Total = 8 + 8 = 16 electrons.
2. **Write the molecular orbital configuration**:
- Filling the orbitals:
- σ1s², σ*1s², σ2s², σ*2s², σ2p_z², π2p_x², π2p_y², π*2p_x¹, π*2p_y¹.
- Total = 2 + 2 + 2 + 2 + 2 + 2 + 1 + 1 = 16 electrons.
3. **Check for unpaired electrons**:
- There are 2 unpaired electrons in the π* orbitals.
- Therefore, O2 is **paramagnetic**.
### Step 3: Analyze B2 (Boron Dimer)
1. **Count the total number of electrons**:
- Boron has 5 electrons, so for B2:
- Total = 5 + 5 = 10 electrons.
2. **Write the molecular orbital configuration**:
- Filling the orbitals:
- σ1s², σ*1s², σ2s², σ*2s², π2p_x¹, π2p_y¹.
- Total = 2 + 2 + 2 + 2 + 1 + 1 = 10 electrons.
3. **Check for unpaired electrons**:
- There are 2 unpaired electrons in the π orbitals.
- Therefore, B2 is **paramagnetic**.
### Step 4: Analyze NO (Nitric Oxide)
1. **Count the total number of electrons**:
- Nitrogen has 7 electrons, and Oxygen has 8 electrons.
- Total = 7 + 8 = 15 electrons.
2. **Write the molecular orbital configuration**:
- Filling the orbitals:
- σ1s², σ*1s², σ2s², σ*2s², σ2p_z², π2p_x², π2p_y², π*2p_x¹.
- Total = 2 + 2 + 2 + 2 + 2 + 2 + 1 = 15 electrons.
3. **Check for unpaired electrons**:
- There is 1 unpaired electron in the π* orbital.
- Therefore, NO is **paramagnetic**.
### Conclusion
After analyzing all the species:
- **CO** is the only species that is **not paramagnetic** (it is diamagnetic).
- The answer to the question is **CO**.
