Which change represents an oxidation reaction?

An oxidation-reduction (redox) reaction is a type of chemical reaction that involves a transfer of electrons between two species.  

Fe+Cu  

2+

⇌Fe  

2+

+Cu

In the above reaction, Fe is oxidised by gaining 2 electrons while Cu is reduced by loosing 2 electrons.

Hence the above reaction is represents an oxidation-reduction reaction.

Hence the required answer is (E)Fe+Cu  

2+  ⇌Fe  

2+  +Cu.

water is used to store them because it would keep the radiation from getting out in the open and causing harm to the workers