2 FeSO4 (aq) + K2S2O8 (aq) → Fe2(SO4)3 (s) + K2SO4 (aq)
This is an oxidation-reduction (redox) reaction:
2 SVII + 2 e- → 2 SVI (reduction)
2 FeII - 2 e- → 2 FeIII (oxidation)
K2S2O8 is an oxidizing agent, FeSO4 is a reducing agent.
This is a precipitation reaction: Fe2(SO4)3 is the formed precipitate.