Why Cr and Cu have abnormally higher 2nd ionisation energy?

Explanation

To understand why chromium (Cr) and copper (Cu) have abnormally higher second ionization energy, we need to analyze their electronic configurations and the stability associated with certain electron arrangements.

### Step-by-Step Solution:

1. **Identify the Atomic Numbers and Electronic Configurations:**
- Chromium (Cr) has an atomic number of 24. Its electronic configuration is:
\[
\text{Cr: } [\text{Ar}] 3d^5 4s^1
...