The oxidation number of Sulphur = +2
Further explanation
General formula for determining Oxidation Numbers :
1. The number of oxidation of single element atoms = 0. Examples of Ar, Mg, Cu, Fe, N₂, O₂, etc. = 0
Group I : +1
Group II : +2
H in compound = +1, except metal hydride compounds (Hydrogen which binds I or II groups) oxidation number H = -1, for example, LiH, MgH₂, etc.
2. Oxidation number O in compound = -2, except OF2 = + 2 and in peroxide (Na₂O₂, BaO₂) = -1 and superoxide, for example KO₂ = -1/2.
3 The oxidation number in a non-filled compound = 0,
The total amount of oxidation in ion = ion charge, Example NO₃⁻ = -1
Sodium thiosulphate - Na₂S₂O₃
Oxidation number Na = +1 ⇒x2 = +2
Oxidation number O = -2 ⇒x3 = -6
Oxidation number Na₂S₂O₃ = 0
2.Na+2.S+3.O=0
2.+1+2.S+3.(-2)=0
2+2S-6=0
-4+2S=0
2S=4
S=+2
