Question

In which of the following elements the 6d orbital is vacant:

• A. Lr
• B. \(\mathrm{Cm}\)
• C. \(\mathrm{Np}\)
• D. \(\mathrm{Fm}\)

Hint:

For actinide electron configurations:
- Check for 5f, 6d, and 7s orbitals.
- 6d orbitals are often partially filled in early actinides.
- Later actinides may skip 6d, filling 5f and 7s.

Answer 1

The Correct Option is D

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): \([Rn] 5f^{14} 6d^1 7s^2\). Has 1 electron in 6d.
- Cm (Curium, Z=96): \([Rn] 5f^7 6d^1 7s^2\). Has 1 electron in 6d.
- Np (Neptunium, Z=93): \([Rn] 5f^4 6d^1 7s^2\). Has 1 electron in 6d.
- Fm (Fermium, Z=100): \([Rn] 5f^{12} 7s^2\). No 6d electrons.
Step 2: Conclusion
Only Fermium (Fm) has a vacant 6d orbital, matching option (D).