In `Ni(CO)_(4)` the oxidation state of Ni is:

Answer

To determine the oxidation state of nickel (Ni) in the complex Ni(CO)₄ (nickel tetra carbonyl), we can follow these steps:

### Step 1: Identify the components of the complex
In the complex Ni(CO)₄, we have:
- Nickel (Ni) as the central metal atom.
- Four carbonyl (CO) ligands attached to it.

### Step 2: Determine the oxidation state of the ligands
Carbonyl (CO) is a neutral ligand, which means it does not contribute any charge to the overall complex. Therefore, the oxidation state of each CO ligand is 0.

### Step 3: Set up the equation for the oxidation state
Let the oxidation state of nickel be represented by \( x \). Since there are four carbonyl ligands, the total contribution to the charge from the ligands is:
\[ 4 \times 0 = 0 \]

The overall charge of the complex Ni(CO)₄ is neutral, which means it is equal to 0. Therefore, we can write the equation:
\[ x + (4 \times 0) = 0 \]

### Step 4: Solve for the oxidation state of nickel
Now, we can simplify the equation:
\[ x + 0 = 0 \]
\[ x = 0 \]

### Conclusion
The oxidation state of nickel (Ni) in the complex Ni(CO)₄ is 0.

---