It seems you're asking about the coefficient of oxygen in the reaction forming phosphorus trioxide (P₂O₃) from phosphorus (P) and oxygen (O₂).

Here's how to figure that out:

The balanced chemical equation:

4 P + 3 O₂ → 2 P₂O₃

Explanation:

* Reactants:

* Phosphorus (P)

* Oxygen (O₂)

* Product:

* Phosphorus trioxide (P₂O₃)

* Coefficients:

* 4 is the coefficient for phosphorus (P).

* 3 is the coefficient for oxygen (O₂). This is the coefficient you're looking for.

* 2 is the coefficient for phosphorus trioxide (P₂O₃).

Therefore, the coefficient of oxygen in the reaction forming phosphorus trioxide from phosphorus and oxygen is 3.