Which has maximum `EAN` of the underbold atoms?
`(Cr=24,Co=27,Fe=26,Ni=28)` .

Options

A. a.`[Cr(EDTA)]^(Θ)`
B. b.`[Co(en)_(3)]^(3+)`
C. c.`[Ni(CN)_(4)]^(2-)`
D. d.`[Fe(C_(2)O_(4))_(3)]^(3-)`

Answer

To find the maximum Effective Atomic Number (EAN) of the given central metal atoms, we will use the formula for EAN:

\[ \text{EAN} = Z - O + 2L \]

Where:
- \( Z \) = Atomic number of the central metal atom
- \( O \) = Oxidation state of the central metal atom
- \( L \) = Number of lone pair donating sites from the ligands

Let's analyze each metal atom one by one.

### Step 1: Calculate EAN for Chromium (Cr)
- Atomic number \( Z = 24 \)
- Oxidation state \( O = +3 \) (due to the presence of a hexadentate ligand)
- Number of lone pair donating sites \( L = 6 \) (hexadentate ligand)

Using the formula:

\[ \text{EAN} = 24 - 3 + 2 \times 6 \]
\[ \text{EAN} = 24 - 3 + 12 = 33 \]

### Step 2: Calculate EAN for Cobalt (Co)
- Atomic number \( Z = 27 \)
- Oxidation state \( O = +3 \) (due to ethylene diamine which is a neutral ligand)
- Number of lone pair donating sites \( L = 6 \) (3 ethylene diamine ligands, each contributing 2)

Using the formula:

\[ \text{EAN} = 27 - 3 + 2 \times 6 \]
\[ \text{EAN} = 27 - 3 + 12 = 36 \]

### Step 3: Calculate EAN for Nickel (Ni)
- Atomic number \( Z = 28 \)
- Oxidation state \( O = +2 \) (due to cyanide ligands)
- Number of lone pair donating sites \( L = 4 \) (4 cyanide ligands, each contributing 1)

Using the formula:

\[ \text{EAN} = 28 - 2 + 2 \times 4 \]
\[ \text{EAN} = 28 - 2 + 8 = 34 \]

### Step 4: Calculate EAN for Iron (Fe)
- Atomic number \( Z = 26 \)
- Oxidation state \( O = +3 \) (due to oxalate ligands)
- Number of lone pair donating sites \( L = 6 \) (3 oxalate ligands, each contributing 2)

Using the formula:

\[ \text{EAN} = 26 - 3 + 2 \times 6 \]
\[ \text{EAN} = 26 - 3 + 12 = 35 \]

### Conclusion
Now, we will summarize the EAN values calculated:

- EAN for Cr = 33
- EAN for Co = 36
- EAN for Ni = 34
- EAN for Fe = 35

The maximum EAN is for Cobalt (Co), which is **36**.

### Final Answer
The central metal atom with the maximum Effective Atomic Number (EAN) is **Cobalt (Co)** with an EAN of **36**.

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