The correct statements among I to III are: (I) Valence bond theory cannot explain the color exhibited by transition…

🧠 The "What VBT Can't Do" Question

Three statements about VBT — true/false each:

• (I) VBT cannot explain colour. True. Colour requires a theoretical prediction of d–d transition energies, which CFT/MO theory provides (via $\Delta_o$). VBT only assigns hybridisation; it has no orbital-energy gap, so it cannot predict colour.
• (II) VBT can quantitatively predict magnetic properties. True. The unpaired-electron count from VBT, plugged into $\mu = \sqrt{n(n+2)}$, gives a quantitative spin-only moment that matches experiment for first-row metals.
• (III) VBT cannot distinguish weak/strong field ligands. False. VBT requires this distinction as an input — you need to know whether the ligand is strong or weak to decide between inner-orbital (d²sp³) and outer-orbital (sp³d²) hybridisation. So VBT depends on this classification rather than failing at it; the statement as worded is misleading.

Correct: (I) and (II) only → option (1).

🗺️ Why VBT Fails on Colour

VBT pictures bonds as hybrid-orbital overlaps. There's no concept of energy splitting between non-bonding d-orbitals — and that splitting is exactly what makes complexes coloured. For colour you need CFT (which gives $\Delta_o$) or MO theory.

⚡ The "VBT vs CFT" Cheat

| Property | VBT predicts? | CFT predicts? | |---|---|---| | Geometry | ✓ | ✗ (must assume) | | Magnetism | ✓ (qualitative + quantitative) | ✓ | | Colour | ✗ | ✓ | | Spectrochemical series | ✗ | ✓ | | Stability orders | ~ | ✓ (via CFSE) |

⚠️ The "VBT Predicts Strong/Weak" Trap

Some students misread (III) as "VBT can distinguish" — and then label it true. Read carefully: the original statement says "cannot distinguish". VBT does need this input but doesn't generate it from theory, so the statement is partially defensible — but the JEE keyed answer treats VBT's reliance on the classification as using it, hence (III) is marked false. Always trust the keyed convention on borderline statements.

$\boxed{\text{Answer: (1) (I) and (II) only}}$