Which of the following rules could explain the presence of three unpaired electrons in N-atom?

Options

A. Hund's rule
B. aufbau's principles
C. Heisenberg's uncertainty principle
D. Pauli's exculsion principle

Answer

To determine which rule explains the presence of three unpaired electrons in a nitrogen atom, we will follow these steps:

### Step-by-Step Solution:

1. **Identify the Atomic Number and Electronic Configuration of Nitrogen**:
- The atomic number of nitrogen (N) is 7. This means it has 7 electrons.
- The electronic configuration of nitrogen is:
\[ 1s^2 \, 2s^2 \, 2p^3 \]

2. **Understand the Electron Distribution in Orbitals**:
- Electrons fill orbitals starting from the lowest energy level to higher energy levels.
- The 1s orbital can hold 2 electrons, and the 2s orbital can also hold 2 electrons.
- After filling the 1s and 2s orbitals, we move to the 2p orbitals.

3. **Fill the 2p Orbitals According to Hund's Rule**:
- The 2p subshell consists of three degenerate orbitals: \(2p_x\), \(2p_y\), and \(2p_z\).
- According to Hund's rule, when filling degenerate orbitals, one electron is placed in each orbital before pairing occurs. This means that each of the three 2p orbitals will receive one electron first.

4. **Count the Unpaired Electrons**:
- After distributing the three electrons in the 2p orbitals, we have:
- \(2p_x\) has 1 electron
- \(2p_y\) has 1 electron
- \(2p_z\) has 1 electron
- Therefore, all three electrons in the 2p orbitals are unpaired.

5. **Conclusion**:
- The presence of three unpaired electrons in the nitrogen atom is explained by **Hund's rule**. This rule states that electrons will fill degenerate orbitals singly and with the same spin before pairing occurs.

### Final Answer:
The rule that explains the presence of three unpaired electrons in the nitrogen atom is **Hund's Rule**.

---