Which of the following species can act as reducing agent ?

Options

A. `[Co(CO)_(4)]^(-)`
B. `Mn(CO)_(6)`
C. `Mn(CO)_(5)`
D. `Cr(CO)_(6)`

Explanation

To determine which of the following species can act as a reducing agent, we need to analyze the effective atomic number (EAN) of each species and see which one can release an electron to achieve a stable noble gas configuration. Here’s a step-by-step solution:

### Step 1: Understand the Concept of Reducing Agents
A reducing agent is a substance that can donate electrons to another substance, thereby reducing that substance while itself being oxidized. In terms of effective atomic number, a reducing agent will have the ability to lose electrons to achieve a stable electronic configuration.

### Step 2: Identify the Species
Let's denote the species we need to analyze. For this example, we will consider:
1. CO₄⁻
2. Mn(CO)₆
3. Mn(CO)₅
4. Cr(CO)₆

### Step 3: Calculate the Effective Atomic Number (EAN) for Each Species
The formula for calculating EAN is:
\[ \text{EAN} = Z - n + \text{(contribution from ligands)} \]
where \( Z \) is the atomic number of the metal, and \( n \) is the oxidation state.

#### For CO₄⁻:
- Atomic number of Cobalt (Co) = 27
- Oxidation state = -1 (since CO is a neutral ligand)
- Contribution from ligands (4 CO) = 4 × 2 = 8 electrons
- EAN = 27 - (-1) + 8 = 27 + 1 + 8 = 36

#### For Mn(CO)₆:
- Atomic number of Manganese (Mn) = 25
- Oxidation state = 0 (neutral ligands)
- Contribution from ligands (6 CO) = 6 × 2 = 12 electrons
- EAN = 25 - 0 + 12 = 25 + 12 = 37

#### For Mn(CO)₅:
- Atomic number of Manganese (Mn) = 25
- Oxidation state = 0 (neutral ligands)
- Contribution from ligands (5 CO) = 5 × 2 = 10 electrons
- EAN = 25 - 0 + 10 = 25 + 10 = 35

#### For Cr(CO)₆:
- Atomic number of Chromium (Cr) = 24
- Oxidation state = 0 (neutral ligands)
- Contribution from ligands (6 CO) = 6 × 2 = 12 electrons
- EAN = 24 - 0 + 12 = 24 + 12 = 36

### Step 4: Analyze the EAN Values
- EAN of CO₄⁻ = 36
- EAN of Mn(CO)₆ = 37
- EAN of Mn(CO)₅ = 35
- EAN of Cr(CO)₆ = 36

### Step 5: Determine Which Species Can Act as a Reducing Agent
A species can act as a reducing agent if it can lose electrons to achieve a stable noble gas configuration. The noble gas configurations are:
- Krypton (Kr) = 36
- Xenon (Xe) = 54

From the calculated EAN values:
- Mn(CO)₆ (EAN = 37) can lose one electron to become 36, which is stable.
- Mn(CO)₅ (EAN = 35) is already stable.
- CO₄⁻ and Cr(CO)₆ have EAN values equal to 36, so they cannot act as reducing agents.

### Conclusion
Thus, the species that can act as a reducing agent is **Mn(CO)₆**.