The correct order of ligands arranged in increasing field strength.

Solution

Chemistry ma’am · 3 steps

Write out the spectrochemical series once, then check every inequality in each option against it.

1. The series. Field strength is how far a ligand splits the d orbitals (Δₒ). Experiment ranks ligands in the spectrochemical series, from weakest to strongest.

   I⁻ < Br⁻ < Cl⁻ < F⁻ < OH⁻ < H₂O < NH₃ < en < CN⁻ < CO

2. Two patterns. Halides get weaker going down the group, so I⁻ is the weakest. Neutral H₂O is stronger than OH⁻, and CN⁻ is near the strong end, above NH₃.

   Option	Where it goes wrong	Verdict
   (a)	Halides reversed: really I⁻ < Br⁻ < F⁻	wrong
   (b)	OH⁻ < H₂O, and CN⁻ is stronger than NH₃	wrong
   (c)	Br⁻ < F⁻ < H₂O < NH₃, every step matches	correct
   (d)	Br⁻ is weaker than both Cl⁻ and OH⁻	wrong

3. So. Only (c) follows the spectrochemical series at every step, so the answer is (c).

The idea to keep. Learn the spectrochemical series as anchors: halides at the weak end (I⁻ weakest), then OH⁻ < H₂O < NH₃ < en, with CN⁻ and CO at the strong end.

Answer from the NTA final answer key. Solution by PrepWiser.