NEET 2022 Chemistry Crystal Field Splitting & Colour MCQ Question

Chapter: Coordination Compounds

Class: 12 | Topic: Crystal Field Splitting & Colour | Difficulty: 🔴 Hard

✅ Ans: A — (iii) > (i) > (ii)

The colour of a complex depends on the energy absorbed for $d-d$ transition:

$$\Delta E=h u$$

Here, ethylenediamine (en) is a stronger-field ligand than $H_2O$:

$$en > H_2O$$

Therefore, more $en$ ligands → larger crystal-field splitting $\Delta$ → higher energy absorbed.

• (iii) $[Ni(en)_3]^{2+}$ → 3 en → maximum $\Delta$
• (i) $[Ni(H_2O)_2(en)_2]^{2+}$ → 2 en → intermediate $\Delta$
• (ii) $[Ni(H_2O)_4(en)_2]^{2+}$ → more $H_2O$ contribution → comparatively lower splitting

$$\boxed{(iii)>(i)>(ii)}$$

📌 NCERT: The colour of transition-metal complexes is due to absorption of visible light for $d-d$ transitions. The energy absorbed depends on the crystal-field splitting $\Delta$.

🧠 NEET Trick: Stronger ligand → larger $\Delta$ → higher energy absorbed.

$$\boxed{en>H_2O}$$

Why Hard 🔴: Requires remembering ligand strength and applying it to compare crystal-field splitting rather than simply identifying a ligand.