Question

Which of the following cannot form stable complexes?

• A. Lanthanides
• B. Actinides
• C. Transition elements
• D. Iron

Answer 1

The correct option is A Lanthanides

In lanthanides $4f$subshell shielded by $5d$ and $6s$ orbitals ,so f orbitals do not participate in bonding, they do not form stable complex. However in actinides $5f$ orbitals extends outwards and participate in bonding. They form stable complex .d - blocks element forms complex frequently too. Hence answer is A.