Which is a spectator ion in the reaction between naoh(aq) and h2so4(aq)?

The reaction between NaOH and H2SO4 is a reaction between an acid and a base which means the reaction is a neutralization that produces products of salt and water. The salt is Na2SO4. 
spectator ions are ions that are found at the both sides of the equation when the aqueous components are in their ionic forms. In this case, when breaking down of components is applied, the spectator ions are Na + and SO4 2- . 

While unproven, it uses facts to support part of a conclusion. it is still factual and has predictive power, however.