1. Assign known oxidation states:

* Ba (Barium): Group 2 elements have a +2 oxidation state.

* O (Oxygen): Oxygen typically has a -2 oxidation state (except in peroxides).

2. Set up an equation:

Let the oxidation state of Cl be "x". Since we have two ClO2 units, we multiply the oxidation state of Cl by 2.

The sum of the oxidation states in a neutral compound must equal zero:

(+2) + 2(x + 2(-2)) = 0

3. Solve for x:

* +2 + 2x - 8 = 0

* 2x - 6 = 0

* 2x = 6

* x = +3

Therefore, the oxidation state of Cl in Ba(ClO2)2 is +3.