A 1:3 electrolyte in aqueous solution is:

Solution & Explanation

Concept: A '1:3 electrolyte' produces ONE cation and THREE anions (total 4 ions, in the ratio 1 cation : 3 anions) on dissociation in water. Only ions OUTSIDE the coordination sphere (counter-ions) ionise; ligands inside the square brackets stay bound and do not ionise. Evaluate each (count ions written outside the brackets): • [CoCl₂(NH₃)₄]Cl → [CoCl₂(NH₃)₄]⁺ + Cl⁻ = 1 cation : 1 anion → 1:1 electrolyte. • [CoCl(NH₃)₅]Cl₂ → [CoCl(NH₃)₅]²⁺ + 2Cl⁻ = 1 cation : 2 anions → 1:2 electrolyte. • [Co(NH₃)₆]Cl₃ → [Co(NH₃)₆]³⁺ + 3Cl⁻ = 1 cation : 3 anions → 1:3 electrolyte. ✓ • [Co(NH₃)₃(NO₂)₃] → all three NO₂⁻ are ligands inside the sphere; no counter-ion → NON-electrolyte. The 1:3 electrolyte is [Co(NH₃)₆]Cl₃ → answer C.