Consider the coordination complex below: The counter ion is:

Question

BlackTom AI · Accepted Answer

Count ligand charges to find the overall complex charge: NH3 is neutral, while Br− and Cl− are anionic ligands (each −1). Let x be the oxidation state of Co.

1) Relevant knowledge points and concepts
- Ammonia (NH3) is a neutral ligand (charge 0).
- Halide ligands (Cl−, Br−) each carry a −1 charge.
- The charge on the coordination complex (inside the brackets) equals (oxidation state of the central metal) + (sum of ligand charges).
- A counter ion outside the brackets balances the overall charge of the coordination compound.

2) Step-by-step reasoning
- Identify ligands from the diagram: 2 NH3, 2 Br, 2 Cl coordinated to Co (octahedral).
- Sum the ligand charges: 2 × (NH3: 0) + 2 × (Br: −1) + 2 × (Cl: −1) = 0 − 2 − 2 = −4.
- Express the complex charge: (charge of Co) + (sum of ligand charges) = complex charge → x + (−4) = complex charge.

3) Intermediate calculation to determine oxidation state and complex charge
- The picture shows a single K outside the brackets as the counter ion. K is K+ (charge +1).
- For electrical neutrality, complex charge + (+1) = 0 → complex charge = −1.
- Solve x − 4 = −1 → x = +3. So the metal is Co(III) and the complex is [Co(NH3)2Br2Cl2]−.

4) Why the correct answer is correct
- Since the coordination sphere carries an overall −1 charge, one K+ counter ion is required. Thus the counter ion is K+ (potassium).

5) Why other options are incorrect
- a. Br and e. Cl: these are coordinated ligands inside the brackets, not separate counter ions.  
- b. NH3: neutral ligand, not a charged counter ion.  
- d. Co: the central metal inside the complex, not an external counter ion.

Conclusion: The counter ion is K, matching the provided correct answer (c. K).

Consider the coordination complex below: The counter ion is:Single choice

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