Calculate the oxidation number of the underlined element in the following ions.
`ul(Cr_(2))O_(7)^(2-)`

Explanation

The oxidation number of the underlined element in the following ions are given below:
`Cr_(2)O_(7)^(2-)`: Let oxidation number of Cr be x, `O= -2, " as " ul(Cr)_(2)O_(7)^(2-)` has charge equal to `-2`, then sum of oxidation no. of all atoms is equal to `-2`. Therefore,
`(x) xx 2 + (-2) xx 7= -2`
`2x= -2 + 14`
`x= + (12)/(2) = +6`
Hence, oxidation number of Cr in `ul(Cr)_(2)O_(7)^(2-)` ion is +6.