Setup the half reactions from the given reaction and balance both simultaneously

Since there's only one reactant from the initial reaction, we can use H₂O as another reactant since this reaction occurs in aqueous conditions. This is necessary so we can make 2 half reactions with different reactants.

Half reactions of HBrO(aq) + H₂O (l)⟶ Br⁻(aq) + O₂(g)   are:

HBrO →  Br⁻ 

H₂O →  O₂

• Balancing this half reactions under acidic conditions follows a particular steps:

Step 1: Balance the non H or O atoms (not necessary)

HBrO →  Br⁻                                           H₂O →  O₂

Step 2: Balance O by adding H₂O on the product side for the 1st eqn. 2nd equation needs 2 Os, add coefficient 2 to H₂O