The number of vacant d-orbitals in completely excited Cl atom is :

Options

A. `2`
B. `3`
C. `1`
D. `4`

Explanation

To determine the number of vacant d-orbitals in a completely excited chlorine (Cl) atom, we need to analyze its electronic configuration in both the ground state and the excited state.

### Step-by-Step Solution:

1. **Identify the Ground State Configuration of Chlorine:**
- The atomic number of chlorine (Cl) is 17. Therefore, the ground state electronic configuration is:
\[ \text{Cl: } 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^5 \]
- In this configuration, we can see that there are no electrons in the d-orbitals (3d).

2. **Understanding Excitation:**
- When we say a chlorine atom is "completely excited," it means that the electrons are promoted to higher energy levels to maximize the number of unpaired electrons for bonding purposes.
- The goal is to maximize the number of unpaired electrons in the valence shell.

3. **Promoting Electrons:**
- In the excited state, we can promote electrons from the 3s and 3p orbitals to the 3d orbitals.
- The 3s orbital has 2 electrons, and the 3p orbital has 5 electrons. To maximize bonding, we can promote some of these electrons to the 3d orbital.

4. **Excited State Configuration:**
- Let's promote 1 electron from the 3s orbital and 2 electrons from the 3p orbital to the 3d orbital. The new configuration will be:
\[ \text{Cl (excited): } 1s^2 \, 2s^2 \, 2p^6 \, 3s^1 \, 3p^3 \, 3d^3 \]
- In this configuration, we have 3 electrons in the 3d orbital.

5. **Counting Vacant d-Orbitals:**
- The d subshell can hold a maximum of 10 electrons (5 orbitals, each can hold 2 electrons).
- Since we have 3 electrons in the 3d orbital, the number of vacant d-orbitals is:
\[ \text{Total d-orbitals} - \text{Occupied d-orbitals} = 5 - 3 = 2 \]

### Final Answer:
The number of vacant d-orbitals in a completely excited chlorine atom is **2**.