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 will follow these steps:

### Step 1: Determine the Atomic Number and Ground State Configuration
The atomic number of chlorine (Cl) is 17. The ground state electronic configuration of chlorine can be written as:
\[ \text{Cl: } 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^5 \]

### Step 2: Identify the First Excited State Configuration
In the first excited state, one of the electrons from the 3p orbital is promoted to the 3d orbital. Therefore, the configuration changes to:
\[ \text{First Excited State: } 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^4 \, 3d^1 \]

### Step 3: Count the Unpaired Electrons
Now we will analyze the unpaired electrons in the first excited state configuration:
- **3s orbital**: 2 electrons (paired)
- **3p orbital**: 4 electrons (the configuration is \(3p^4\), which means there are 4 electrons in the 3p subshell. According to Hund's rule, the 4th electron will pair with one of the existing electrons, leaving 2 unpaired electrons.)
- **3d orbital**: 1 electron (unpaired)

Now, we can summarize the unpaired electrons:
- From the 3p orbital: 2 unpaired electrons
- From the 3d orbital: 1 unpaired electron

### Step 4: Total Unpaired Electrons
Adding the unpaired electrons from both orbitals:
\[ \text{Total Unpaired Electrons} = 2 \, (\text{from } 3p) + 1 \, (\text{from } 3d) = 3 \]

Thus, the number of unpaired electrons present in the first excited state of the chlorine atom is **3**.

### Final Answer
The number of unpaired electrons in the first excited state of a chlorine atom is **3**.

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