In BrO-2, the oxidation number of Br can be determined as follows:

Let x be the oxidation number of Br.

Oxygen has an oxidation number of -2. There are two oxygen atoms in BrO-2, so the total contribution from oxygen is 2 × (-2) = -4.

To balance the overall charge of the ion, which is -2, the oxidation number of Br must be:

x + (-4) = -2

x = -2 + 4

x = +2

Therefore, the oxidation number of Br in BrO-2 is +2.