Which of the following is paramagnetic?

Options

A. `O_2^(-)`
B. `CN^(-)`
C. `NO^(+)`
D. `CO`

Explanation

To determine which of the given species is paramagnetic, we need to analyze the electron configurations of each option. A species is considered paramagnetic if it has unpaired electrons in its molecular orbital configuration.

### Step-by-Step Solution:

1. **Identify the Species**: The options provided are:
- O2⁻ (superoxide ion)
- CN⁻ (cyanide ion)
- CN⁺ (cyanide cation)
- CO (carbon monoxide)

2. **Count the Electrons for Each Species**:
- **O2⁻**: Oxygen has 8 electrons, and since O2 has 16 electrons, O2⁻ will have 17 electrons (16 + 1).
- **CN⁻**: Carbon has 6 electrons and nitrogen has 7 electrons, so CN⁻ has 14 electrons (6 + 7 + 1).
- **CN⁺**: CN⁺ has one less electron than CN⁻, so it has 13 electrons.
- **CO**: Carbon has 6 electrons and oxygen has 8 electrons, so CO has 14 electrons (6 + 8).

3. **Determine the Electron Configuration**:
- **O2⁻**: The electron configuration can be written as:
- σ2s² σ*2s² σ2p² π2p_x² π2p_y² π*2p_x² π*2p_y¹
- Here, there is 1 unpaired electron in the π*2p_y orbital, indicating that O2⁻ is paramagnetic.

- **CN⁻**: The electron configuration is:
- σ2s² σ*2s² σ2p² π2p_x² π2p_y²
- All electrons are paired, indicating that CN⁻ is diamagnetic.

- **CN⁺**: The electron configuration is:
- σ2s² σ*2s² σ2p² π2p_x²
- All electrons are paired, indicating that CN⁺ is diamagnetic.

- **CO**: The electron configuration is:
- σ2s² σ*2s² σ2p² π2p_x² π2p_y²
- All electrons are paired, indicating that CO is diamagnetic.

4. **Conclusion**: Among the options, only O2⁻ has unpaired electrons, making it the only paramagnetic species.

### Final Answer:
The paramagnetic species is **O2⁻**.