Explain why transition elements have many irregularities in their electronic configuration.

Explanation

### Step-by-Step Solution:

1. **Understanding Transition Elements**: Transition elements are defined as the d-block elements in the periodic table, which include elements that have partially filled d-orbitals.

2. **Energy Levels of Orbitals**: In transition metals, there is a small energy difference between the (n-1)d orbitals and the ns orbitals. This means that the energy levels of the d orbitals and the s orbitals of the outermost shell are very close to each other.

3. **Electron Configuration**: Due to the small energy difference, when electrons are added to transition metals, they can occupy either the (n-1)d orbitals or the ns orbitals. This leads to irregularities in the expected order of filling the orbitals according to the Aufbau principle.

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