Which of the following is paramagnetic?

Options

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

Explanation

To determine which of the given molecules is paramagnetic, we need to analyze the number of electrons in each molecule and check for unpaired electrons. A molecule is considered paramagnetic if it has unpaired electrons.

### Step-by-step Solution:

1. **Understand Paramagnetism**:
- Paramagnetic substances have unpaired electrons. To identify if a molecule is paramagnetic, we need to check the electron configuration and count the number of unpaired electrons.

2. **Count Total Electrons**:
- For the molecules provided, we will count the total number of electrons and determine if they are even or odd. An odd number of total electrons indicates the presence of unpaired electrons, suggesting that the molecule is paramagnetic.

3. **Analyze Each Molecule**:
- **CO (Carbon Monoxide)**:
- Carbon (C) has 6 electrons: 1s² 2s² 2p²
- Oxygen (O) has 8 electrons: 1s² 2s² 2p⁴
- Total electrons in CO = 6 (C) + 8 (O) = 14 (even)
- Conclusion: CO is **not paramagnetic**.

- **O₂²⁻ (Oxide Ion)**:
- Each oxygen atom has 8 electrons, and there are two oxygen atoms, plus 1 additional electron due to the 2- charge.
- Total electrons = 8 + 8 + 1 = 17 (odd)
- Conclusion: O₂²⁻ is **paramagnetic**.

- **CN⁻ (Cyanide Ion)**:
- Carbon (C) has 6 electrons, and nitrogen (N) has 7 electrons, plus 1 additional electron due to the -1 charge.
- Total electrons = 6 + 7 + 1 = 14 (even)
- Conclusion: CN⁻ is **not paramagnetic**.

- **NO⁺ (Nitric Oxide cation)**:
- Nitrogen (N) has 7 electrons, and oxygen (O) has 8 electrons, minus 1 electron due to the +1 charge.
- Total electrons = 7 + 8 - 1 = 14 (even)
- Conclusion: NO⁺ is **not paramagnetic**.

4. **Final Conclusion**:
- Among the molecules analyzed, only **O₂²⁻** is paramagnetic due to having an odd number of total electrons, indicating the presence of unpaired electrons.