To determine which of the given species is paramagnetic, we need to analyze the number of electrons in each species and their electron configurations. Paramagnetic substances have unpaired electrons, while diamagnetic substances have all paired electrons.
### Step-by-Step Solution:
1. **Identify the species and their electron counts**:
- O2⁻ (Oxygen anion)
- CN⁻ (Cyanide ion)
- N4⁺ (Nitrogen cation)
- CO (Carbon monoxide)
2. **Calculate the number of electrons for each species**:
- **O2⁻**: Oxygen has 8 electrons each, so for O2, we have 8 + 8 = 16. The extra electron from O2⁻ gives us 17 electrons.
- **CN⁻**: Carbon has 6 electrons and nitrogen has 7 electrons. Adding these gives 6 + 7 = 13. The extra electron from CN⁻ gives us 14 electrons.
- **N4⁺**: Each nitrogen has 7 electrons, so for 4 nitrogen atoms, we have 4 × 7 = 28. Since it's N4⁺, we lose one electron, giving us 27 electrons.
- **CO**: Carbon has 6 electrons and oxygen has 8 electrons, giving us 6 + 8 = 14 electrons.
3. **Determine the molecular orbital configurations**:
- **For O2⁻ (17 electrons)**:
- The molecular orbital filling will be:
- 1s², 1s*², 2s², 2s*², 2pσ², 2pπ², 2pπ², 2pσ*¹ (the last one represents the unpaired electron).
- Since there is one unpaired electron, O2⁻ is **paramagnetic**.
- **For CN⁻ (14 electrons)**:
- The molecular orbital filling will be:
- 1s², 1s*², 2s², 2s*², 2pσ², 2pπ², 2pπ² (all electrons are paired).
- Since there are no unpaired electrons, CN⁻ is **diamagnetic**.
- **For N4⁺ (27 electrons)**:
- The molecular orbital filling will be:
- 1s², 1s*², 2s², 2s*², 2pσ², 2pπ², 2pπ², 2pσ*² (all electrons are paired).
- Since there are no unpaired electrons, N4⁺ is **diamagnetic**.
- **For CO (14 electrons)**:
- The molecular orbital filling will be:
- 1s², 1s*², 2s², 2s*², 2pσ², 2pπ², 2pπ² (all electrons are paired).
- Since there are no unpaired electrons, CO is **diamagnetic**.
4. **Conclusion**:
- Among the given species, only **O2⁻** is paramagnetic due to the presence of one unpaired electron.
### Final Answer:
**O2⁻ is paramagnetic.**
