Oxidation numbers of P in ` PO_4^(3-)`, of S in ` SO_4^(2-)`, and that of `Cr` in ` Cr_2O_7^(2-)` are respectively ,

Options

A. ` +3, +6` and `+6`
B. ` +5, +6` and `+6`
C. ` +3. +6`, and `+5`
D. ` +5. +3`, and `+6`

Answer

B

Explanation

Let x be the oxidation number of P in ` PO_4^(3-)`
` x+4 (-2) =-3`
` x-8 =-3`
or ` x= + 5`
Let x be the oxidation number of S in ` SO_4^(2-)` :
` x +4 (-2) =-2`
` x-8 =-2`
` x = +6`
Let x be the oxidation number of ` Ci` in ` Cr_2O_7^(2-) `:
` 2x+7 (-2) =-2`
` 2x -14 =-2`
` 2x = 12`
` x= +6 `
In all the three cases, we have used the rule that the sum of all oxidation numbers in a polyatomic ion must equal the charge on the ion.