The number of unpaired electrons in magnesium atom is

Options

A. 0
B. 1
C. 2
D. 3

Answer

To determine the number of unpaired electrons in a magnesium atom, we can follow these steps:

### Step 1: Identify the Atomic Number
The atomic number of magnesium (Mg) is 12. This means that a magnesium atom has 12 electrons.

### Step 2: Determine the Electron Configuration
Using the Aufbau principle, we fill the electron orbitals in order of increasing energy. The order of filling is as follows:
- 1s
- 2s
- 2p
- 3s

Now, we can fill the orbitals:
- 1s can hold 2 electrons: **1s²**
- 2s can hold 2 electrons: **2s²**
- 2p can hold 6 electrons: **2p⁶**
- 3s can hold 2 electrons: **3s²**

So, the complete electron configuration for magnesium is:
\[ \text{Mg: } 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \]

### Step 3: Identify the Valence Electrons
The valence electrons are the electrons in the outermost shell. For magnesium, the outermost shell is the 3rd shell, which contains the 3s orbital. The 3s orbital has 2 electrons.

### Step 4: Determine the Pairing of Electrons
In the 3s orbital, there are 2 electrons. According to the Pauli Exclusion Principle, these two electrons will occupy the same orbital but will have opposite spins. Therefore, they are paired.

### Step 5: Count the Unpaired Electrons
Since both electrons in the 3s orbital are paired, there are no unpaired electrons in the magnesium atom.

### Conclusion
The number of unpaired electrons in a magnesium atom is **0**.

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