On the basis of symmetry (n-a) `d^(4) ns^(2)` and `(n-1) d^(9) ns^(2)` configurations are less stable and immediately change over to the corresponding more stable (n-1) `d^(5) ns^(1) " and" (n-1) d^(10) ns^(1)` configurations .Are there any exceptions to this generalization ? Comment

Explanation

To address the question regarding the stability of electron configurations and exceptions to the generalization, we can break down the solution into clear steps:

### Step 1: Understand the Electron Configurations
The electron configurations mentioned are:
- (n-1)d^4 ns^2
- (n-1)d^9 ns^2
- (n-1)d^5 ns^1
- (n-1)d^10 ns^1
...