K2SO4 would because Fe2(SO4)3 is a blue precipitate.
Reaction with Fe(NO3)3 and KOH would make Fe(OH)3, which is insoluble. So that would be the precipitate formed. All others would dissociate because they are soluble.
Disregard the other answers on this page. K2SO4 (#3) is the wrong answer because it is soluble.
It’s not K2SO4, it’s KOH! 🙂