Presence of three unpaired electrons in phosphorus atom can be explained by

Options

A. Pauli's rule
B. Uncertainty principle
C. Aufbau's rule
D. Hund' rule.

Answer

To explain the presence of three unpaired electrons in a phosphorus atom, we can follow these steps:

### Step 1: Determine the Atomic Number
The atomic number of phosphorus (P) is 15. This means that a phosphorus atom has 15 electrons.

### Step 2: Write the Electronic Configuration
The electronic configuration of phosphorus can be written as follows:
- 1s² 2s² 2p⁶ 3s² 3p³

### Step 3: Analyze the Electron Distribution
From the electronic configuration:
- The first shell (1s) is filled with 2 electrons.
- The second shell (2s and 2p) is filled with 8 electrons (2 in 2s and 6 in 2p).
- The third shell has 2 electrons in 3s and 3 electrons in 3p.

### Step 4: Identify the Unpaired Electrons
In the 3p subshell, there are 3 electrons. According to Hund's rule, electrons will occupy degenerate orbitals singly before pairing up. Therefore, the three electrons in the 3p subshell will each occupy separate orbitals, resulting in three unpaired electrons.

### Step 5: Apply Hund's Rule
Hund's rule states that when electrons are added to orbitals of the same energy (like the three 3p orbitals), they will fill each orbital singly before any orbital gets a second electron. This leads to the presence of three unpaired electrons in phosphorus.

### Conclusion
Thus, the presence of three unpaired electrons in a phosphorus atom can be explained by **Hund's rule**.

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