Question

What is the oxidation number of sulfur in \[{H_2}S\]?
A. +1
B. +2
C. -2
D. -1

Answer 1

Hint: One must know that the sum of the oxidation numbers in a compound must be equal to zero. If the oxidation state of any constituent of a molecule is known, the other one can be determined by considering their sum as zero.

Complete step-by-step answer:
Oxidation state shows the gain or loss of electrons of an atom when it forms a chemical bond with another atom. We can also call it an oxidation number. The transfer of electrons can be described by the oxidation of the molecules.
There are certain rules to be followed to know the oxidation state of an atom:
The oxidation state of an atom is zero in a neutral compound which has atoms of a single element, such as, an oxygen molecule has zero oxidation number.
To find the oxidation number of an atom in a compound, one must know that the overall charge on the compound is always equal to the sum of oxidation states of all atoms in the compound. Using this equation, the unknown value of oxidation number of an atom can be determined if other values are given.
The oxidation state of an atom depends on which atom the bond is shared with. For example, if an atom is more electronegative, it will gain more electrons and that will be its oxidation number accordingly.
Using these rules let us find the oxidation state of sulphur in hydrogen sulphide. Firstly, we should note that the hydrogen state of hydrogen is +1, due to its less electronegativity. We know that the overall charge on hydrogen sulphide is zero. Therefore,
Overall charge on \[{H_2}S\] = 2(oxidation state of hydrogen) + oxidation state of sulphur
0 = 2(+1) + oxidation state of sulphur
Thus, Oxidation state of sulphur = -2

Hence, the correct option is (C).

Note: The oxidation state of hydrogen is +1 when we combine it with non-metals such as methane, ammonia, water, etc. if hydrogen is combined with metals such as alkali hydrides, its oxidation state is -1. This is due to electronegativity of hydrogen which lies in between metals and nonmetals.