Which of the following has the highest molar conductivty?

potassium hexacyanoferrate(II)

The correct answer is Option (1) → potassium hexacyanoferrate(II)

Molar conductivity (Λm\Lambda_mΛm​) depends on the number of ions in solution and their mobility:

1. K₄[Fe(CN)₆] → 4 K⁺ + [Fe(CN)₆]⁴⁻ → total 5 ions
2. [Cr(H₂O)₆]Cl₂ → [Cr(H₂O)₆]²⁺ + 2 Cl⁻ → total 3 ions
3. [Co(NH₃)₄Cl₂]Cl → [Co(NH₃)₄Cl₂]⁺ + Cl⁻ → total 2 ions
4. K₂[Ni(CN)₄] → 2 K⁺ + [Ni(CN)₄]²⁻ → total 3 ions

• More ions → higher molar conductivity.
• Therefore, K₄[Fe(CN)₆] produces the most ions and has the highest molar conductivity.