Calculate the oxidation number of S and C respectively in,
(i) `S_(2)O_(7)^(-2)`
(ii) `CO_(2)`

Explanation

(i) Let the oxidation number of S in `S_(2)O_(7)^(-2)` be x. As `S_(2) O_(7)^(-2)` is a negative ion,
`therefore` Sum of oxidation number of atoms = charge on ion
`[(x,-2),(S_(2),O_(7))]^(2-)`
`(x xx 2) + (-2 xx 7) = -2`
`2x - 14 = -2 " "2x = 12" "x = +6`
`therefore` oxidation number of S in `S_(2)O_(7)^(2-)` is +6.
(ii) Let the oxidation number of C in `CO_(2)` be x. Since `CO_(2)` is a neutral molecule.
`{:(x,-2),(C,O_(2)):}`
`x + (-2 xx 2) = 0`
x - 4 = 0 or x = +4
`therefore` oxidation number of C in `CO_(2)` is +4.