Question

The oxidation number of $\text{ Na}$ in$\text{ NaCl}$:
A) $0$
B) $-1$
C) $+1$
D) $2$
E) $+2$

Answer 1

Hint: The net charge on the neutral molecules is always equal to zero and the sum of the oxidation state of the elements present in the molecules or species is always equal to the charge. Here, sodium chloride is a neutral molecule and the chlorine shows an oxidation state of$-1$.

Complete step by step answer:
The oxidation number is defined as the charge which is allocated to the atom or element in a chemical reaction. The charge on the atom may be due to the gain or loss of electrons. In short, the oxidation number is the charge on the atom which appears when it forms an ionic bond with the tom. It helps to describe the transfer of electrons from one element to another.
In molecules, the electronegative atoms gain an electron from other less electronegative species and thus its oxidation number decreases by the number of electrons acquired by it.
There are certain guidelines to determine the oxidation number of the element. Oxidation number is either positive or negative.
 1) The atoms which exist in its elemental form have zero oxidation number.
 2) Elements which exist as a single atom or monatomic have oxidation number equal to their charge.
3) In a species, the sum of the oxidation number of all the atoms is equal to the charge on the species.
4) Net charge on the neutral molecules is always equal to zero.
Now, we can find out the oxidation state of sodium $\text{ Na}$ in$\text{ NaCl}$.
This $\text{ NaCl}$ is the neutral molecule. Therefore the net charge which is present on the $\text{ NaCl}$is equal to the zero (Step 4)
We know that the oxidation state of the molecules is equal to the sum of the oxidation number of all elements present in the molecule is equal to the charge. Since then $\text{ NaCl}$has zero charge. We can say that the sum of the oxidation number of $\text{ Na}$and $\text{Cl}$will be equal to zero. It is as shown below,
$\begin{align}
  & \text{Charge on NaCl = oxidation number of Na + Oxidation number of Cl} \\
 & \text{ 0 = oxidation number of Na + Oxidation number of Cl } \\
\end{align}$
 $\text{Cl}$ Is more electronegative than the$\text{ Na}$. It gains an electron to form an ionic bond. Therefore the oxidation state of chlorine is $-1$ .
Let us substitute these values .We get the oxidation state of$\text{ Na}$.
$\begin{align}
  & \text{ 0 = oxidation number of Na + Oxidation number of Cl } \\
 & \text{ 0 = oxidation number of Na + (-1) } \\
 & \text{ oxidation number of Na = 0 - (-1) = +1 } \\
\end{align}$
Therefore the oxidation number $\text{ NaCl}$ is equal to$\text{+1}$. The $\text{ Na}$atoms lose their electrons to the chlorine to form an ionic bond.

Hence, (C) is the correct option.


Note: Oxidation number can be also referred to as the oxidation state. However there is a difference between the terms. The oxidation state represents the charge on the atom if all the bonds are ionic. Each atom will exhibit a unique oxidation state. However, the oxidation number term is widely used in coordination chemistry .It refers to the charge acquired by the central atom in its free state (no ligand state)