Oxidation number of cr in cr2o7

There are seven oxygen atoms, so the total charge is −2⋅7=−14 . So, twochromium atoms have a total oxidation number of +12 . Since one is not more electronegative than the other, we can divide the number by two to get onechromium’s oxidation number. So, achromium atom here has an oxidation number of +6 .