Calculate the oxidation number of nickel in `Ni(CO)_4` iron in `Fe(CO)_5` and carbon in `CH_2O`.

Explanation

To calculate the oxidation numbers of nickel in Ni(CO)₄, iron in Fe(CO)₅, and carbon in CH₂O, we will follow a systematic approach for each compound.

### Step 1: Calculate the oxidation number of nickel in Ni(CO)₄

1. **Identify the oxidation state of CO**: Carbon monoxide (CO) is a neutral molecule. Therefore, its oxidation number is 0.

2. **Set up the equation**: Let the oxidation number of nickel (Ni) be \( x \). The formula for nickel tetracarbonyl is Ni(CO)₄. Since there are 4 CO molecules, we can write the equation:
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