Which of the following obey EAN rule?

Options

A. `[Co(NH_(3))_(6)]^(3+)`
B. `Cr(CO)_(6)`
C. `[V(CO)_(6)]^(-)`
D. `[Zn(EDTA)]^(-2)`

Explanation

To determine which of the following complexes obey the Effective Atomic Number (EAN) rule, we will calculate the EAN for each complex using the formula:

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

Where:
- \( Z \) = atomic number of the central metal atom
- \( O \) = oxidation state of the central atom
- \( L \) = number of lone pair donating sites (number of ligands that donate a pair of electrons)

Let's analyze each complex step by step.

### Step 1: Calculate EAN for Cobalt Complex
1. **Identify the central atom and its atomic number**: Cobalt (Co) has an atomic number of 27.
2. **Determine the oxidation state**: The ligand NH3 is neutral, so the oxidation state of Co in this complex is +3.
3. **Count the lone pair donating sites**: NH3 donates 1 lone pair, and if there are 6 NH3 ligands, then there are 6 lone pair donating sites.
4. **Plug values into the EAN formula**:
\[ \text{EAN} = 27 - 3 + 2 \times 6 = 27 - 3 + 12 = 36 \]

### Step 2: Calculate EAN for Chromium Complex
1. **Identify the central atom and its atomic number**: Chromium (Cr) has an atomic number of 24.
2. **Determine the oxidation state**: The ligand CO is neutral, so the oxidation state of Cr in this complex is 0.
3. **Count the lone pair donating sites**: CO donates 1 lone pair, and there are 6 CO ligands, so there are 6 lone pair donating sites.
4. **Plug values into the EAN formula**:
\[ \text{EAN} = 24 - 0 + 2 \times 6 = 24 + 12 = 36 \]

### Step 3: Calculate EAN for Vanadium Complex
1. **Identify the central atom and its atomic number**: Vanadium (V) has an atomic number of 23.
2. **Determine the oxidation state**: The complex has a -1 charge, and CO is neutral, so the oxidation state of V is +1.
3. **Count the lone pair donating sites**: There are 6 CO ligands, so there are 6 lone pair donating sites.
4. **Plug values into the EAN formula**:
\[ \text{EAN} = 23 - 1 + 2 \times 6 = 23 - 1 + 12 = 34 \]

### Step 4: Calculate EAN for Zinc Complex with EDTA
1. **Identify the central atom and its atomic number**: Zinc (Zn) has an atomic number of 30.
2. **Determine the oxidation state**: The oxidation state of Zn in this complex with EDTA is +2 (EDTA is a hexadentate ligand and carries a -4 charge).
3. **Count the lone pair donating sites**: EDTA has 6 lone pair donating sites.
4. **Plug values into the EAN formula**:
\[ \text{EAN} = 30 - 2 + 2 \times 6 = 30 - 2 + 12 = 40 \]

### Summary of EAN Results
- Cobalt Complex: EAN = 36
- Chromium Complex: EAN = 36
- Vanadium Complex: EAN = 34
- Zinc Complex (EDTA): EAN = 40

### Conclusion
The complexes that obey the EAN rule should have an EAN equal to the atomic number of the nearest noble gas. In this case, the complexes with EAN of 36 (Cobalt and Chromium) obey the EAN rule, while the Vanadium complex does not, and the Zinc complex with EDTA does not either.

### Final Answer
The complexes that obey the EAN rule are:
- Cobalt Complex
- Chromium Complex