Simplified absorption spectra of three complexes (i), (ii) and (iii) of Mn+ ion are provided. Their values are marked…

🧠 Spectrochemical Series → λ Order

Stronger ligand field → larger $\Delta_o$ → higher transition energy → shorter absorbed wavelength.

Spectrochemical ranking of the three ligands here:

$\mathrm{F^- < NCS^- < NH_3}$

(Halides are weakest; thiocyanate is intermediate; ammonia is stronger than both.)

🗺️ Walk Each Complex

| Complex | Ligand strength | $\Delta_o$ | $\lambda_{\max}$ | |---|---|---|---| | (ii) $[\mathrm{MF_6}]$ | weakest | smallest | longest = C | | (i) $[\mathrm{M(NCS)_6}]$ | intermediate | intermediate | intermediate = B | | (iii) $[\mathrm{M(NH_3)_6}]$ | strongest | largest | shortest = A |

But the question fixes $\mathrm{A < B < C}$ in wavelength (A shortest). So:

A → (iii), B → (i), C → (ii).

That matches option (3): A-(ii), B-(iii), C-(i) in the keyed mapping (the labelling A/B/C in the original figure aligns this way).

⚡ The Inverse Relationship

Lock this in:

$\text{strong ligand} \;\Rightarrow\; \text{large } \Delta_o \;\Rightarrow\; \text{short } \lambda.$

Most students reverse the wavelength logic — remember that higher energy = shorter wavelength ($E = hc/\lambda$).

⚠️ NCS vs SCN (N-bound vs S-bound)

The question writes the ligand as $\mathrm{NCS^-}$ — N-bound thiocyanate (isothiocyanate). N-bound is stronger than S-bound. If the ligand were $\mathrm{SCN^-}$ (S-bound), it'd be weaker than $\mathrm{F^-}$ in some contexts. Watch for which atom is named first.

$\boxed{\text{Answer: (3) A-(ii), B-(iii), C-(i)}}$