How can I make it to where every player gets an item after killing an entity?

I am using a PC, and was wondering what code to put to make it to where if a player kills a mob, they get a certain item, an example of this would be:

• Kill a zombie=Get a gold ore
• Kill a skeleton=Get a dirt block,
  Ect.

I am asking this because I am making a server world, and want to add a reputation sort of a thing to show how many mobs someone has killed.