`H_(3) PO_(3) = H_(3) PO_(4) + PH_(3)`

Explanation

To balance the redox reaction \( H_3PO_3 \rightarrow H_3PO_4 + PH_3 \), we will follow these steps:

### Step 1: Determine Oxidation States
First, we need to determine the oxidation states of phosphorus in both \( H_3PO_3 \) and \( H_3PO_4 \) and \( PH_3 \).

- In \( H_3PO_3 \):
\[
H: +1 \quad (3 \text{ H}) \quad P: x \quad O: -2 \quad (3 \text{ O})
...