Which transition elements in the first transition series have anomalous electron configurations?

Chromium and Copper

Explanation:

Atomic number of Cr = 24

As per the Aufbau principle Electronic configuration of Cr should be as follow:

Cr: [Ar] 3d4 4s2

However, actual configuration is as follows:

Cr: [Ar] 3d5 4s1

This is because half filled orbitals are more stable.

Atomic number of Cu = 29

As per the Aufbau principle Electronic configuration of Cu should be as follow:

Cu: [Ar] 3d9 4s2

However, actual configuration is as follows:

Cu: [Ar] 3d10 4s1

This is because fully filled orbitals are more stable.

Therefore, Cr and Cu have anomalous configuration.