Calculate the oxidation number of the underlined element in the following ions.
`ul(P)O_(4)^(3-)`

Explanation

To calculate the oxidation number of phosphorus (P) in the ion \( PO_4^{3-} \), we can follow these steps:

### Step 1: Assign the oxidation number to phosphorus
Let the oxidation number of phosphorus be \( x \).

### Step 2: Assign the oxidation number to oxygen
The oxidation number of oxygen is generally \( -2 \).

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