Outer electronic configuration of Eu in ground state is:

Question

Accepted Answer

The outer electronic configuration of europium (Eu) in its ground state is correctly given by Option 1: $4f^{7}6s^{2}$. Here's a detailed explanation supporting this choice and why the other options are incorrect:

1. **Explanation for Option 1 ($4f^{7}6s^{2}$):**
   - Europium is an element in the lanthanide series, with an atomic number of 63. The lanthanides are characterized by the filling of the 4f subshell.
   - In the ground state, europium has a partially filled 4f subshell. Specifically, it has seven electrons in the 4f subshell, which is denoted as $4f^{7}$.
   - Additionally, europium has two electrons in the 6s subshell, denoted as $6s^{2}$.
   - Therefore, the correct outer electronic configuration for europium in its ground state is $4f^{7}6s^{2}$, making Option 1 the correct choice.

2. **Explanation for why the other options are incorrect:**

- **Option 2 ($4f^{7}5d^{1}6s^{2}$):**
     - This configuration suggests that there is one electron in the 5d subshell. However, in the ground state of europium, the 5d subshell is not occupied. The 4f subshell is filled before the 5d subshell in the lanthanides, and europium does not have an electron in the 5d subshell in its ground state.

- **Option 3 ($4f^{7}6s^{0}$):**
     - This configuration implies that there are no electrons in the 6s subshell, which is incorrect for europium. In its ground state, europium has two electrons in the 6s subshell, as indicated by $6s^{2}$.

- **Option 4 ($4f^{5}6s^{2}$):**
     - This configuration suggests that there are only five electrons in the 4f subshell. However, europium in its ground state has seven electrons in the 4f subshell, not five. Therefore, this option does not accurately represent the electronic configuration of europium.

In conclusion, Option 1 ($4f^{7}6s^{2}$) is the correct outer electronic configuration for europium in its ground state, as it accurately reflects the distribution of electrons in the 4f and 6s subshells.