`EAN` of cobalt is 36 in `[Co(NH_(3))_(2)O_(2)(en)br]` Thus `O_(2)` is .

Options

A. dioxide
B. superoxide ion
C. peroxide ion
D. oxide

Answer

To find the oxidation state of the oxygen in the complex `[Co(NH₃)₂O₂(en)Br]`, we can follow these steps:

### Step 1: Understand the Effective Atomic Number (EAN) Formula
The formula for the Effective Atomic Number (EAN) is given by:
\[ \text{EAN} = Z - x + 2y \]
where:
- \( Z \) = atomic number of the central metal atom (cobalt in this case)
- \( x \) = oxidation number of the central metal atom
- \( y \) = number of lone pair donating sites from the ligands

### Step 2: Identify the Atomic Number of Cobalt
The atomic number of cobalt (Co) is 27.

### Step 3: Set Up the EAN Equation
We know that the EAN of cobalt is 36. Therefore, we can set up the equation:
\[ 36 = 27 - x + 2y \]

### Step 4: Determine the Lone Pair Donating Sites
Now, we need to calculate \( y \), the total number of lone pair donating sites from the ligands:
- **NH₃**: Each NH₃ has 1 lone pair, and there are 2 NH₃ ligands, contributing \( 2 \) lone pairs.
- **O₂**: O₂ can donate 1 lone pair (as it exists in the form of a peroxide ion, O₂²⁻).
- **en (ethylene diamine)**: This ligand has 2 nitrogen atoms, each donating 1 lone pair, contributing \( 2 \) lone pairs.
- **Br**: Bromine (Br) is a neutral ligand and contributes \( 1 \) lone pair.

Now, summing these up:
- From 2 NH₃: 2 lone pairs
- From O₂: 1 lone pair
- From en: 2 lone pairs
- From Br: 1 lone pair

Total lone pair donating sites \( y = 2 + 1 + 2 + 1 = 6 \).

### Step 5: Substitute Values into the EAN Equation
Now substitute \( y = 6 \) into the EAN equation:
\[ 36 = 27 - x + 2(6) \]
\[ 36 = 27 - x + 12 \]
\[ 36 = 39 - x \]

### Step 6: Solve for the Oxidation State of Cobalt
Rearranging gives:
\[ x = 39 - 36 \]
\[ x = 3 \]

So, the oxidation state of cobalt is +3.

### Step 7: Determine the Oxidation State of O₂
Next, we can find the oxidation state of O₂ in the complex. The overall charge of the complex is neutral (0). The contributions from the ligands are:
- NH₃: 0 (neutral)
- en: 0 (neutral)
- Br: -1 (as it is a negatively charged ligand)

Let \( y \) be the oxidation state of O₂. The equation becomes:
\[ +3 + 0 + 0 - 1 + y = 0 \]
\[ 3 - 1 + y = 0 \]
\[ 2 + y = 0 \]
\[ y = -2 \]

### Conclusion
Thus, the oxidation state of O₂ in the complex is -2, indicating that O₂ exists as the peroxide ion (O₂²⁻).

### Final Answer
O₂ is in the form of a peroxide ion (O₂²⁻).

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