Final answer:
The oxidation number of Br in NaBrO is -1.
Step-by-step explanation:
Both reactants are the elemental forms of their atoms, so the Na and Br atoms have oxidation numbers of 0. In the ionic product, the Na+ ions have an oxidation number of +1, while the Br- ions have an oxidation number of -1.
Sodium is increasing its oxidation number from 0 to +1, so it is being oxidized; bromine is decreasing its oxidation number from 0 to -1, so it is being reduced.
Since the oxidation number of Br is -1, we can conclude that the oxidation number of Br in NaBrO is -1.