Calculate the oxidation number of phosphorous in H3PO4.
let us consider the oxidation number of phosphorous to be x.
also, we know that the oxidation number of hydrogen is +1
the oxidation number of oxygen is -2.
(+1) × 3 + x + (-2 ) × 4 = 0
+3 + x – 8 = 0
x – 5 = 0
x = 0
Hence the oxidation number of P in H3PO4 is + 5.