The number of unpaired electrons present in the first excited state of chlorine atom is

Options

A. 1
B. 3
C. 5
D. 2

Answer

To determine the number of unpaired electrons present in the first excited state of a chlorine atom, we can follow these steps:

### Step 1: Determine the Ground State Electronic Configuration
Chlorine (Cl) has an atomic number of 17. The electronic configuration of chlorine in its ground state is:
- **1s² 2s² 2p⁶ 3s² 3p⁵**

This can also be expressed in a condensed form:
- **[Ne] 3s² 3p⁵**

### Step 2: Identify the Valence Electrons
In the ground state, the valence shell for chlorine is the third shell (n=3), which contains:
- 2 electrons in the 3s subshell
- 5 electrons in the 3p subshell

### Step 3: Count the Unpaired Electrons in Ground State
In the 3p subshell, the configuration can be represented as:
- **3p: ↑↓ ↑ ↑ ↑ ↑**
This shows that there are 5 electrons in the 3p subshell, where:
- 2 electrons are paired (in the 3p orbital)
- 3 electrons are unpaired

Thus, in the ground state, chlorine has **3 unpaired electrons**.

### Step 4: Excite One Electron to a Higher Energy Level
When energy is provided to the chlorine atom, one of the unpaired electrons from the 3p subshell can be excited to a higher energy subshell, which is the 3d subshell. The new configuration in the first excited state will be:
- **3s² 3p⁴ 3d¹**

### Step 5: Count the Unpaired Electrons in the First Excited State
In the first excited state:
- The 3s subshell still has 2 paired electrons.
- The 3p subshell now has 4 electrons, which can be represented as:
- **3p: ↑↓ ↑ ↑ ↑**
- This shows that there are now **4 electrons in the 3p subshell, with 4 unpaired electrons**.
- The 3d subshell has 1 electron, which is unpaired.

### Final Count of Unpaired Electrons
Adding the unpaired electrons:
- From 3p: 4 unpaired electrons
- From 3d: 1 unpaired electron

Thus, in the first excited state of chlorine, the total number of unpaired electrons is:
- **4 (from 3p) + 1 (from 3d) = 5 unpaired electrons**

### Conclusion
The number of unpaired electrons present in the first excited state of a chlorine atom is **5**.

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