Question
The correct statement among the following is:
JEE Main
Chemistry
Coordination Compounds
2026
JEE Main 2026 (28 January Shift 1)
JEE Main Chemistry Question (2026) — Solution
Options
- A. Ni ( CO )_ 4 and [ Ni ( CN )_ 4 ]^ 2- are diamagnetic and [ NiCl _ 4 ]^ 2- is paramagnetic.
- B. Ni ( CO )_ 4 and [ NiCl _ 4 ]^ 2- are diamagnetic and [ Ni ( CN )_ 4 ]^ 2- is paramagnetic.
- C. [ Ni ( CN )_ 4 ]^ 2- and [ NiCl _ 4 ]^ 2- are diamagnetic and Ni ( CO )_ 4 is paramagnetic.
- D. Ni ( CO )_ 4 is diamagnetic and [ NiCl _ 4 ]^ 2- and [ Ni ( CN )_ 4 ]^ 2- are paramagnetic.
Answer
A. Ni ( CO )_ 4 and [ Ni ( CN )_ 4 ]^ 2- are diamagnetic and [ NiCl _ 4 ]^ 2- is paramagnetic.
Step-by-step solution
In Ni(CO)_4, Nickel is in 0 oxidation state with configuration [Ar]3d^8 4s^2. CO is a strong field ligand, causing pairing of 4s electrons into 3d orbitals, resulting in 3d^ 10 configuration. It is sp^3 hybridized and diamagnetic (zero unpaired electrons). In [Ni(CN)_4]^ 2- , Nickel is in +2 oxidation state with configuration [Ar]3d^8. CN^- is a strong field ligand, causing pairing of the two unpaired electrons in 3d orbitals. It is dsp^2 hybridized (square planar) and diamagnetic. In [NiCl_4]^ 2- , Nickel is in +2 oxidation state with configuration [Ar]3d^8. Cl^- is a weak field ligand and cannot cause pairing of electrons. It has two unpaired electrons in 3d orbitals, making it sp^3 hybridized (tetrahedral) and paramagnetic. Therefore, Ni(CO)_4 and [Ni(CN)_4]^ 2- are diamagnetic, while [NiCl_4]^ 2- is paramagnetic.
Related: Chemistry — Coordination Compounds · All PYQ Banks