Question

The electronic configuration of actinides cannot be assigned with a degree of certainty because of:

• A. The small energy difference between $5f$ and $6d$ orbitals
• B. Overlapping of inner orbitals
• C. Free movement of electrons over all the orbitals
• D. None of above

Answer 1

The correct option is A The small energy difference between $5f$ and $6d$ orbitals

Actinides are mainly $f$-block elements with some exception. The series mostly correspond to the filling of $5f$ orbital. The $5f$ and $6d$ orbitals have comparable energy with equal $n+l$ value. Therefore it is difficult to assign their electronic configuration with a degree of certainty.