Electronic Configuration

Chromium (Cr) has an atomic number of 24, which means it has 24 electrons. The electron configuration of chromium is: From this, we can see that the electrons in the outermost shell (the 4th shell) are and . Therefore, chromium has 6 valence electrons, with one electron in the orbital and five electrons in the orbitals.

The 6d orbital is part of the electronic configuration of actinides. We need to check the electron configurations of Lr, Cm, Np, and Fm to find which has no electrons in the 6d orbital.
Step 1: Electron configurations
- Lr (Lawrencium, Z=103): . Has 1 electron in 6d.
- Cm (Curium, Z=96): . Has 1 electron in 6d.
- Np (Neptunium, Z=93): . Has 1 electron in 6d.
- Fm (Fermium, Z=100): . No 6d electrons.
Step 2: Conclusion
Only Fermium (Fm) has a vacant 6d orbital, matching option (D).