Identify the least stable among the following

Options

A. `Li^(-)`
B. `Be^(-)`
C. `B^(-)`
D. `C^(-)`

Explanation

To identify the least stable species among the given options, we will analyze the electron configurations of each species and determine their stability based on the principles of electron configuration and stability.

### Step-by-Step Solution:

1. **Identify the Electron Configuration of Lithium (Li):**
- Lithium (Li) has an atomic number of 3. Its electron configuration is:
\[ \text{Li: } 1s^2 2s^1 \]

2. **Determine the Configuration of Lithium Ion (Li⁺):**
- When lithium loses one electron to form Li⁺, the configuration becomes:
\[ \text{Li}^+: 1s^2 \]
- This configuration is stable because the 1s orbital is fully filled.

3. **Identify the Electron Configuration of Beryllium (Be):**
- Beryllium (Be) has an atomic number of 4. Its electron configuration is:
\[ \text{Be: } 1s^2 2s^2 \]

4. **Determine the Configuration of Beryllium Ion (Be⁻):**
- When beryllium gains one electron to form Be⁻, the configuration becomes:
\[ \text{Be}^-: 1s^2 2s^2 2p^1 \]
- This configuration is less stable because it introduces an electron into a new p orbital, which is not half-filled or fully filled.

5. **Identify the Electron Configuration of Boron (B):**
- Boron (B) has an atomic number of 5. Its electron configuration is:
\[ \text{B: } 1s^2 2s^2 2p^1 \]

6. **Determine the Configuration of Boron Ion (B⁻):**
- When boron gains one electron to form B⁻, the configuration becomes:
\[ \text{B}^-: 1s^2 2s^2 2p^2 \]
- This configuration is relatively stable as it does not significantly change the stability.

7. **Identify the Electron Configuration of Carbon (C):**
- Carbon (C) has an atomic number of 6. Its electron configuration is:
\[ \text{C: } 1s^2 2s^2 2p^2 \]

8. **Determine the Configuration of Carbon Ion (C⁻):**
- When carbon gains one electron to form C⁻, the configuration becomes:
\[ \text{C}^-: 1s^2 2s^2 2p^3 \]
- This configuration is stable as it achieves a half-filled p subshell.

9. **Conclusion:**
- Among the configurations analyzed, Be⁻ (Beryllium ion) has the least stable configuration due to the presence of an electron in a new p orbital, which is less stable compared to the other configurations.

### Final Answer:
The least stable species among the given options is **Be⁻ (Beryllium ion)**.