IMAT 2015 Q47 [Oxidation Numbers]

Assume that the oxidation numbers are as shown below:

N = –3
H = +1
Cr = +6
O = –2

Which compound formula given below is correct?

A. [ (NH_4)_2CrO_4 ] ^+
B. NH_4Cr_2O_7
C. (NH_4)_2CrO_4
D. [ (NH_4)_3CrO_4 ] ^–
E. (NH_4)_3CrO_4