What is the oxidation number of Na2CrO4?

The oxidation number of Na in Na2CrO4 is +1 and the oxidation number of O in Na2CrO4 is -2. To find the oxidation number of Cr, we let x be the oxidation number: 2(+1) + x + 4(-2) = 0 x = +6

Therefore, the oxidation number of Cr in Na2CrO4 is +6.