RE-NEET 2026 Chemistry Lanthanides MCQ Question

The principle to determine the number of unpaired electrons in lanthanide ions is to analyze their electron configurations. For Ho³⁺ (Holmium ion), the electron configuration is $[Xe] 4f^8$. In this configuration, there are four unpaired electrons in the 4f subshell.

Calculating the unpaired electrons, we find that the 4f subshell can hold a maximum of 14 electrons, and with 8 electrons present, the arrangement leads to 4 unpaired electrons.

The other options fail because:

• Ce³⁺ has 3 unpaired electrons,
• Tb³⁺ has 3 unpaired electrons,
• Nd³⁺ has 3 unpaired electrons.

Thus, only Ho³⁺ has four unpaired electrons.