What is the oxidation state of Cr in Cr 2 O7 2- ?

+ 6

Explanation:

The sum of the oxidation numbers in Cr2O72-, a polyatomic ion, is -2, the charge of the ion.

There are seven oxygen atoms, so the total charge is − 2⋅7 = − 14.

Let x be the oxidation number of two chromium atoms. x + ( − 14 ) = − 2 x−14 = −2 x = 12

Two chromium atoms have a total oxidation number of + 12. we can divide the number by two to get one chromium’s oxidation number. 12/2 = 6

So, a chromium atom here has an oxidation number of + 6.

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