Among `KO_(2), KAlO_(2), CaO_(2) and NO_(2)^(+)`, unpaired electrons is present in :

Options

A. `NO_(2)^(+) and CaO_(2)`
B. `KO_(2) and KAlO_(2)`
C. `KO_(2)` only
D. `CaO_(2)` only

Answer

To determine which of the given compounds has unpaired electrons, we will calculate the total number of valence electrons for each compound. If the total number of electrons is odd, the compound will have unpaired electrons. If it is even, all electrons are paired.

### Step-by-Step Solution:

1. **Calculate the total number of electrons for KO₂ (Potassium Superoxide)**:
- Potassium (K) has an atomic number of 19, which means it has 19 electrons.
- Oxygen (O) has an atomic number of 8. Since there are 2 oxygen atoms, we have \(8 \times 2 = 16\) electrons.
- Total electrons in KO₂ = \(19 + 16 = 35\).

2. **Calculate the total number of electrons for KAlO₂ (Potassium Aluminum Oxide)**:
- Potassium (K) has 19 electrons.
- Aluminum (Al) has an atomic number of 13, contributing 13 electrons.
- Oxygen (O) has 8 electrons, and with 2 oxygen atoms, we have \(8 \times 2 = 16\) electrons.
- Total electrons in KAlO₂ = \(19 + 13 + 16 = 48\).

3. **Calculate the total number of electrons for CaO₂ (Calcium Peroxide)**:
- Calcium (Ca) has an atomic number of 20, contributing 20 electrons.
- Oxygen (O) has 8 electrons, and with 2 oxygen atoms, we have \(8 \times 2 = 16\) electrons.
- Total electrons in CaO₂ = \(20 + 16 = 36\).

4. **Calculate the total number of electrons for NO₂⁺ (Nitronium Ion)**:
- Nitrogen (N) has an atomic number of 7, contributing 7 electrons.
- Oxygen (O) has 8 electrons, and with 2 oxygen atoms, we have \(8 \times 2 = 16\) electrons.
- Since it is a positive ion (NO₂⁺), we subtract 1 electron.
- Total electrons in NO₂⁺ = \(7 + 16 - 1 = 22\).

5. **Determine which compounds have unpaired electrons**:
- KO₂ has 35 electrons (odd) → **unpaired electrons**.
- KAlO₂ has 48 electrons (even) → **no unpaired electrons**.
- CaO₂ has 36 electrons (even) → **no unpaired electrons**.
- NO₂⁺ has 22 electrons (even) → **no unpaired electrons**.

### Conclusion:
Among the compounds KO₂, KAlO₂, CaO₂, and NO₂⁺, only KO₂ has unpaired electrons.

### Final Answer:
**KO₂ only**.

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