Question

The oxidation number of Cl in $C{{l}_{2}}$ is:
(A) 0
(B) -1
(C) +1
(D) -2
(E) +2

Answer 1

Oxidation number is the charge when an atom is present in a combined state with other atoms. In the elemental state, the oxidation number of an atom or molecule will be zero.

Complete step by step solution:
The oxidation number of an element is defined as the charge on an atom of the element that has in its ion or appears to have when present in the combined state with other atoms. We can call the oxidation number also as an oxidation state.
Some rules applied for the determination of oxidation number of an atom are:
The oxidation number of all the atoms of different elements in their respective elementary state and allotropic forms is always zero. For example, $He,{{N}_{2}},{{H}_{2}}$, etc.
In monatomic ions, the oxidation number is equal to the charge of the ion. For example, the oxidation number of $A{{l}^{3+}}$ion is +3 and the oxidation number of ${{S}^{2-}}$ion is -2.
In most of the compounds, the oxidation number of hydrogen is taken as +1. And in most of the compounds, the oxidation number of oxygen is taken as -2. The oxidation number of alkali metal ions is taken +1 and the oxidation number of halogen is taken -1.
The Cl in $C{{l}_{2}}$is 0 because the chlorine molecule is in its elemental state. If it gains electrons then the oxidation number will be -1 and if it donates electrons then the oxidation number will be +1.

Hence, the correct answer is an option (A) “0”.

Note: In neutral molecules, the sum of the oxidation number of all atoms is zero and in complexions, the sum of the oxidation numbers of all the atoms in the ion is always equal to the charge on the ion.