Which of the following complexes has six coordination number?

Options

A. `[Zn(CN)_4]^(2-)`
B. `[Co(en)_2Cl_2]^+`
C. `[Ag(NH_3)_2]^+`
D. `[Ni(NH_3)_4]^(2+)`

Answer

To determine which of the given complexes has a coordination number of 6, we need to analyze the ligands present in each complex and their ability to coordinate with the central metal atom.

### Step-by-Step Solution:

1. **Identify the Ligands**:
- The first complex contains cyanide (CN^-), which is a monodentate ligand. This means it can bind to the metal at only one site.
- The second complex contains ethylenediamine (en) and chloride ions (Cl^-). Ethylenediamine is a bidentate ligand, meaning it can bind at two sites.

2. **Count the Coordination from Ligands**:
- For the first complex (with cyanide), if there are 4 cyanide ligands, the coordination number will be:
\[ \text{Coordination Number} = 4 \times 1 = 4 \]
- For the second complex (with ethylenediamine and chloride), we analyze it as follows:
- Ethylenediamine (en) contributes:
\[ 2 \text{ (from one en)} \times 2 \text{ (since there are 2 en)} = 4 \]
- Chloride ions (Cl^-) contribute:
\[ 2 \text{ (since there are 2 Cl^-)} \]
- Therefore, the total coordination number for the second complex is:
\[ \text{Total Coordination Number} = 4 + 2 = 6 \]

3. **Conclusion**:
- The first complex has a coordination number of 4, while the second complex has a coordination number of 6. Thus, the complex with a coordination number of 6 is the second option.

### Final Answer:
The complex with a coordination number of 6 is the second option (cobalt with ethylenediamine and chloride).

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