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Question
Calculate the oxidation number of the underlined atom.
Cr2O72−
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Solution
Cr2O72−
Oxidation of O = –2
\[\ce{Cr2O^2-_7}\] is an ionic species.
∴ Sum of the oxidation numbers of all atoms = – 2
∴ 2 × (Oxidation number of Cr) + 7 × (Oxidation number of O) = – 2
∴ 2 × (Oxidation number of Cr) + 7 × (–2) = – 2
∴ 2 × (Oxidation number of Cr) – 14 = – 2
∴ 2 × (Oxidation number of Cr) = – 2 + 14
∴ Oxidation number of Cr = `+12/2`
∴ Oxidation number of Cr in \[\ce{Cr2O^2-_7}\] = +6
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