* Oxygen's Oxidation State: Oxygen typically has an oxidation state of -2.

* Overall Charge: The ion has a charge of -3.

* Setting up the Equation: Let 'x' represent the oxidation state of boron. We can write the equation:

x + 3(-2) = -3

* Solving for x:

x - 6 = -3

x = +3

Therefore, the oxidation state of Boron in BO3^-3 is +3.