Question

The valency of oxygen in $N{a_2}{O_2}$ is:
A. $+ 1$
B. $+ 2$
C. $- 2$
D. $- 1$

Answer 1

Valency is the measure of the combining capacity of atoms or molecules. Therefore, it is the capacity of an atom of a single element to react and combine with particular numbers of atoms of another element. Electrons in an atom are arranged in different orbitals. The electrons present in the outermost shell are called valence shell electrons.

Complete step by step answer:
Now we will discuss it in detail.
$N{a_2}{O_2}$ which is also known as Sodium Peroxide. In sodium peroxide, the valency or the oxidation state of oxygen is $- 1$.
When we assign oxidation number, we assign conceptual charges to the individual atoms such that these charges are summed up we get the charge on the molecule or the ion. Thus, elements have an oxidation number of 0, because they are assumed not to have donated or accepted electrons (the process which defines oxidation and reduction) respectively.

For sodium peroxide we have $N{a_2}{O_2}$. To calculate the oxidation state of the oxygen we know that sodium generally has an oxidation state of $+ 1$ in salts and it does so here.

The compound is $N{a_2}{O_2}$
$\Rightarrow 2 \times 1 + 2 \times oxidation\,number\,of\,O = 0$
$\Rightarrow 2 \times oxidation\;number\;of\;O = - 2$
$\Rightarrow oxidation\,number\,of\,O = - 1$

For two sodium atoms, the charge will be 2 and after calculation, we got the oxidation state of oxygen $- 1$.
Therefore the oxidation state of oxygen in sodium peroxide is $- 1$.

So, the correct answer is Option D.

Note: Sodium peroxide can be used to bleach the wood pulp as that is used for the production of paper and textiles.
It is used for specialized laboratory operations (For example- the extraction of minerals from various ores).
In some preparations, it is also used as an oxidizing agent.
When it reacts with carbon dioxide it produces oxygen and sodium carbonate so it is considered as a source of oxygen.