The spectator ion in the given complete ionic equation is K+.
In this reaction, when we break the compounds into their ionic forms, we can see which ions participate in the chemical reaction and which do not. Ag+ and Br− combine to form the precipitate AgBr(s), indicating they are the ions that are actively participating in the reaction. Meanwhile, K+ and NO3− do not change during the reaction—they remain in the aqueous phase as ions and are not involved in forming a solid product. Therefore, they are classified as spectator ions because they are present in the solution but do not affect the overall reaction.