Question

What is the oxidation number of $S$ in ${H_2}S{O_3}$ ?

Answer 1

The compound that can release a proton is known as an acid. Hydrogen, sulphur, and oxygen combine with each other and form an acid known as sulphurous acid. These atoms can also form an acid known as sulphuric acid but the oxidation number of sulphur atoms is different in both these acids.

Complete answer:
Oxidation number is defined as the number that was assigned to an atom in the chemical compound given by the number of electrons gained or lost when involved in bond formation with other atoms in that molecule.
Sulphurous acid was represented by the molecular formula of ${H_2}S{O_3}$ Generally, acids containing a central metal atom with high oxidation state can have the suffix as -ic acid. The acid containing a central metal atom with low oxidation state can have the suffix as -ous acid.
Oxidation number of Sulphur in sulphuric acid can be determined from the hydrogen atoms and oxygen atom in sulphurous acid. Each hydrogen atom carries the charge of $+ 1$ and each oxygen atom carries the charge of $- 2$
The oxidation number of sulphur in sulphuric acid is $2\left( 1 \right) + x + 3\left( { - 2} \right) = 0 \Rightarrow x = + 4$
Thus, the oxidation number of sulphur in sulphuric acid is $+ 4$

Note:
For some atoms, the oxidation number will be negative and the oxidation number of any diatomic molecule is zero. If the oxidation number is positive, then the atom loses electrons. Oxidation is defined as the loss of electrons. Sulphur in Sulphuric acid undergoes oxidation.