The complete ionic equation for the reaction between H2SO4(aq) and CaI2(aq) to form CaSO4(s) and 2HI(aq) is:

2H+ (aq) + SO42-(aq) + Ca2+ (aq) + 2I-(aq) → CaSO4(s) + 2H+(aq) + 2I-(aq)

In this equation, the spectator ions, which do not participate in the reaction, are H+ and I-. The net ionic equation, which shows only the species that undergo chemical change, is:

SO42-(aq) + Ca2+ (aq) → CaSO4(s)