"Coordination Compounds" — Medium JEE chemistry MCQ
**[JEE Mains 2026]** Arrange the following metal ions in increasing order of number of unpaired electrons in their low spin octahedral complexes: Mn²⁺, Cr³⁺, Fe²⁺, Co³⁺
- A. Co³⁺ < Mn²⁺ < Fe²⁺ < Cr³⁺
- B. Co³⁺ < Fe²⁺ < Mn²⁺ < Cr³⁺
- C. Fe²⁺ = Co³⁺ < Cr³⁺ < Mn²⁺
- D. Co³⁺ = Fe²⁺ < Mn²⁺ = Cr³⁺
Solution
In low spin complexes, electrons pair up in t₂g before filling eₔ.
Co³⁺ (d⁶): t₂g⁶ eₔ⁰ → 0 unpaired electrons
Fe²⁺ (d⁶): t₂g⁶ eₔ⁰ → 0 unpaired electrons
Cr³⁺ (d³): t₂g³ eₔ⁰ → 3 unpaired electrons
Mn²⁺ (d⁵): t₂g⁵ eₔ⁰ → 1 unpaired electron
Order: Fe²⁺ = Co³⁺ < Mn²⁺ < Cr³⁺