Which complex act as R.A.

Options

A. `[Cu(NH_3)_4]^(2+)`
B. ` [Co(NH_3)_6]^(2+)`
C. `[Fe(CN)_6]^(4-)`
D. both (1), (2)

Answer

To determine which complex acts as a reducing agent (R.A.), we need to evaluate the effective atomic number (EAN) of each complex. A complex can act as a reducing agent if it can donate electrons, which is possible when its EAN is greater than the atomic number of the nearest noble gas.

**Step-by-step solution:**

1. **Identify the complexes and their components:**
- We have the following complexes to analyze:
- A) Cu(NH3)2^+
- B) Co(NH3)6^2+
- C) Fe(CN)6^4-
- D) Both 1 and 2

2. **Calculate the Effective Atomic Number (EAN) for each complex:**
- The formula for EAN is:
\[ \text{EAN} = x - y + z \]
where:
- \(x\) = atomic number of the metal
- \(y\) = oxidation state of the metal
- \(z\) = total electrons donated by ligands

3. **Calculate EAN for Cu(NH3)2^+:**
- Atomic number of Cu = 29
- Oxidation state of Cu in this complex = +2
- Number of NH3 ligands = 2 (each NH3 donates 2 electrons)
- Total electrons donated by ligands = \(2 \times 2 = 4\)
- EAN calculation:
\[ \text{EAN} = 29 - 2 + 4 = 31 \]
- The nearest noble gas atomic number is 36 (Krypton). Since 31 is less than 36, Cu(NH3)2^+ cannot act as a reducing agent.

4. **Calculate EAN for Co(NH3)6^2+:**
- Atomic number of Co = 27
- Oxidation state of Co in this complex = +2
- Number of NH3 ligands = 6 (each NH3 donates 2 electrons)
- Total electrons donated by ligands = \(6 \times 2 = 12\)
- EAN calculation:
\[ \text{EAN} = 27 - 2 + 12 = 37 \]
- The nearest noble gas atomic number is 36. Since 37 is greater than 36, Co(NH3)6^2+ can act as a reducing agent.

5. **Calculate EAN for Fe(CN)6^4-:**
- Atomic number of Fe = 26
- Oxidation state of Fe in this complex = +2 (since CN is a -1 ligand and there are 6 CN ligands)
- Total charge from ligands = -6 (from 6 CN)
- Therefore, oxidation state of Fe = 26 - 6 = +2
- Number of CN ligands = 6 (each CN donates 2 electrons)
- Total electrons donated by ligands = \(6 \times 2 = 12\)
- EAN calculation:
\[ \text{EAN} = 26 - 2 + 12 = 36 \]
- The nearest noble gas atomic number is 36. Since EAN equals 36, Fe(CN)6^4- is stable and does not act as a reducing agent.

6. **Conclusion:**
- Only Co(NH3)6^2+ can act as a reducing agent. Therefore, the correct answer is option B.