Calculate the oxidation number of sulfur in H₂S₂O₇.

Explanation

Taking hydrogen as +1 and oxygen as −2, electrical neutrality gives 2(+1) + 2x + 7(−2) = 0 for H₂S₂O₇. Thus 2x = 12 and each sulfur has oxidation number +6. Oxidation number is a formal electron-accounting quantity.