[Moss]

determine the oxidation number if chromium in Cr(NO3)3

N=-3
O=-2

so (NO3)3= -3 -3(2)
=-9 *3
=-27 ?

im not sure about the oxidation numbers i assigned to N and O
help thanks

[UG]

I think it would be easier to do it with the ions involved,
NO₃^- is the nitrate ion, since the overall charge of the anion is -1, you don't need to worry about the O's and the N's as they are unimportant. So since there are three nitrate anions, their total oxidation number is -1 x 3 = -3 so it makes sense that the O.N of the chromium is....

[yukiheart]

the oxidation numbers are :
Cr : +3
O : -2
N : +5
so 1*(+3) + [(+5)*1 + (-2)*3]*3 =0