An oxidation number is a number that is assigned to an atom in a substance. The oxidation number could be positive, negative, or zero depending on if the electrons are lost or gained.
Generally Oxygen has -2 oxidation number because it gains 2 electrons.
and a hydrogen atom has +1 oxd. no.
Based on the above info, we can calculate for others.
a) CO2
x + 2 (-2) = 0 [We equate with 0 because net charge is 0)
so, x = +4
Carbon ox. no. is = +4
b) H2SO4
2(+1) + x + 4 (-2) = 0
2 +x - 8 = 0
so, x = 6 (sulphur)
c) (PO4)3-
x +4(-2) = -3
x = +5 (Phophorus)
d) (MnO4)2-
x + 4(-2) = -2
x = +6 (Manganese)
