Calculate the oxidation number of the following compounds.
Cr in `K_(2)Cr_(2)O_(7)`

Explanation

(i) Let the oxidation number of Cr be x.
`{:(+1,,x,,-2),(K_(2),,Cr_(2),,O_(7)),((+1 xx 2),+,(x xx 2),+,(-2 xx 7)=0):}`
2 + 2x - 14 = 0
2x = 12
x = +6
`therefore` oxidation number of Cr in `K_(2)Cr_(2)O_(7)` is +6.
(ii) Let the oxidation number of P be x.
`{:(+1,,x,,-2),(H_(3),,P,,O_(4)),((+1 xx 3),+,x,+,(-2 xx 4) = 0):}`
3 + x - 8 = 0
x = +5
`therefore` oxidation number of P in `H_(3)PO_(4)` is +5.