[magicalatom]

which is capable of oxidizing Cu (s) to Cu+2 (aq) when added to Cu (s) in solution?
A. Al+3 (aq)
B. Ag+ (aq)
C. Ni (s)
D. I- (aq)
E. Au+3 (aq)

Answer: B

I chose D. at first because of the negative charge wanting to take H's but that is wrong because negative charge means it already has extra electrons so I would need to pick something very positive.  So my second answer choice after I figured out the mistake I made was choice Al+3 over Au+3 but i am not sure exactly why. 

I do know oxidizing agent is something that will become reduced, but how do you figure this one out?  Do I need to memorize reduction potentials?

Any ideas, can someone guide me through this please?

I wanted to add, I think I know why it is Ag+ because it is 4d10 electron configuration so taking 2 from Cu it will fill its shell to 4d105s2 so the s2 is complete.  I think this is the special trend with this element where the d orbital will fill to 10 and the s will be 1 instead of 4d9s2  Cr and Mo do something similar instead of 3d4s2 its 3d5s1 the exception is Cr, Mo, Cu, Ag and Au

[clinz63]

In a way, you have to memorize which one is the most easily oxidized - the reactivity series.

https://en.wikipedia.org/wiki/Reactivity_series

There is a mnemonic though. The one that I know of is

Little(Li) Peter(K) Barry(Ba) Carl(Ca) Saw(Na) Magneto(Mg) A(Al) Manzy(Mn) Zebra(Zn) Carrying(Cr) Iron(Fe) Nails(Ni) To(Tin) Liverpool(Pb). He(H) Caught(Cu) Billy(Bi) A(Sb) Mexican(Hg) Silver(Ag) Plated(Pt) Goat(Au).

http://ptarongoy.tripod.com/sitebuildercontent/sitebuilderfiles/chmrxnshandout.pdf