Q. The d electron configurations of Cr²⁺, Mn²⁺, Fe²⁺ and Ni²⁺ are 3d⁴, 3d⁵, 3d⁶ and 3d⁸ respectively. Which one of the following aqua complexes will exhibit the minimum paramagnetic behaviour? (At. No. Cr = 24, Mn = 25, Fe = 26, Ni = 28)
A) [Fe(H₂O)₆]²⁺
B) [Ni(H₂O)₆]²⁺
C) [Cr(H₂O)₆]²⁺
D) [Mn(H₂O)₆]²⁺
Explanation
[Solution from source] H₂O is a weak-field ligand, so the ions stay high-spin: Cr²⁺ (d⁴) 4, Mn²⁺ (d⁵) 5, Fe²⁺ (d⁶) 4 and Ni²⁺ (d⁸) 2 unpaired electrons. [Ni(H₂O)₆]²⁺ has the fewest, so it is least paramagnetic; [Mn(H₂O)₆]²⁺ is the most. Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.