Question

Oxidation number of $S$ in $S_2{O}_3^{2-}$ is
(A). $-2$
(B). $+2$
(C). $+6$
(E). $0$

Answer 1

Hint:Oxidation number is also known as oxidation state and is defined as the charge which an atom has either gained or lost in comparison to the neutral compound. It is also referred to the degree of oxidation of any atom or compound.

Complete step by step answer:
We know that the oxidation number of an element may be defined as the charge which an atom of the element has in its ion appears to have when present in the combined state with other atoms. Oxidation numbers are also called oxidation states. There are spume rules that should be applied to determine the oxidation number of an atom in an ion molecule. The oxidation number of all the atoms of deficient all allotropic form is taken to be zero.
For eg $N_2$,$C{l}_2$,$H_2$,$He$,etc. the oxidation number of each atom is zero. The oxidation number of monoatomic the association number of hydrogen is when combined with non-metal and is -1 when combined with actual metals called metal hydrides. The oxidation number of oxygen is -2 in most of its compounds, except in peroxide. In neutral compounds, the sum of the oxidation number of all atoms is zero. In complex ions the sum of the oxidation number of all the atoms in the ion is equal to the charge on the ion.
Now we have to find the oxidation number of S in $s_2{o}_3^{2-}$[Thiosulphate ion] white structure.

Let the oxidation number of sulfur $\left(S\right)$ in $S_2{O}_3^{2-}$ $x$. Since I atoms of $S$ are present, so the combined oxidation number of $S$ virile be $2x$. We know that the oxidation number of oxygen is$-2$. Since 3 atoms of oxygen are present, so its combined oxidation number will be$3(-2)=-6$. Now this ion contains a charge of$-2$, where the sum of the oxidation number of all atoms in an atom is equal to$-2$.
I.e. $2x+\left(-6\right)=-2$
$2x=-2+6$
$2x=4$
$x=+2$
So the oxidation number of $S$ in $S_2{O}_3^{2-}$ should be $+2.$

Note:
Since there is no peroxide linkage present in the above compound, we have taken the oxidation state of oxygen as $-2$. If peroxide linkage was present, then we should have taken its oxidation number to be -1.