Assign oxidation # for...?

Question

Ok, please help me determine the oxidation #s for :
(also, include how you got your answer please)

NaOH

and

Na4 As O4
I assigned the following oxidations #s to the one above:
Na---> +1
As---> +4
O4---> -2
Please tell me if I'm correct.

Answer 1

I suggest that the compound is Na3AsO4, that As = +5. Otherwise, you're just fine!