Chemistry query??? 10 points

Hello. I am doing GCSE chemistry at the moment and interested in one of my questions concerning the reaction of iron (II) sulphate and sodium hydroxide. When writing the ionic equation, you find that the green precipitate formed turns brown after a whil, because the iron 2+ ion is oxidised and forms an iron 3+ ion. Why does this ion get oxidised, to turn the solution brown?

Thanks for any help :)

it oxidizes because oxygen is being released and is reacting with the iron in the solution. Water is an excellent medium for reactions to occur