In the third excited state the number of unparied electrons in chlorine atom is

Options

A. 5
B. 7
C. 3
D. 1

Explanation

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

### Step-by-Step Solution:

1. **Identify the Atomic Number of Chlorine**:
- Chlorine has an atomic number of 17, which means it has 17 electrons.

2. **Write the Ground State Electronic Configuration**:
- The electronic configuration of chlorine in its ground state is:
\[ 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^5 \]
- This shows that there are 2 electrons in the 3s subshell and 5 electrons in the 3p subshell.

3. **Determine Unpaired Electrons in Ground State**:
- In the ground state, the 3p subshell has 5 electrons. The distribution is:
- 3p: ↑↓ ↑ ↑ ↑ ↑ (2 paired, 3 unpaired)
- Therefore, there are **3 unpaired electrons** in the ground state.

4. **Excite the Electrons**:
- In the first excited state, one of the 3p electrons will be promoted to the 3d subshell:
\[ 3s^2 \, 3p^4 \, 3d^1 \]
- In this state, there are **3 unpaired electrons** (2 in 3p and 1 in 3d).

5. **Second Excited State**:
- In the second excited state, another 3p electron is excited to the 3d subshell:
\[ 3s^2 \, 3p^3 \, 3d^2 \]
- Here, there are still **3 unpaired electrons** (2 in 3d and 1 in 3p).

6. **Third Excited State**:
- In the third excited state, one of the paired electrons from the 3s subshell is excited to the 3d subshell:
\[ 3s^1 \, 3p^3 \, 3d^3 \]
- Now, we have:
- 3s: 1 unpaired electron
- 3p: 3 unpaired electrons
- 3d: 3 unpaired electrons

7. **Count Total Unpaired Electrons**:
- Adding them up:
- 1 (from 3s) + 3 (from 3p) + 3 (from 3d) = **7 unpaired electrons**.

### Final Answer:
The number of unpaired electrons in the third excited state of a chlorine atom is **7**.