Question

What is the oxidation number of sodium $(Na)$ in pure sodium, $Na$?

Answer 1

Oxidation number is the total number of electrons that an atom gains or losses in order to form a chemical bond with another atom. Oxidation number is also known as oxidation state.

Complete step by step answer:
Every atom that participates in oxidation-reduction reactions is assigned an oxidation number that reflects its ability to gain, donate or share electrons; but a neutral substance has an oxidation number of zero since it has no electron to lose, gain or share with another atom.
Here, the given atom is sodium in its pure form $(Na)$. The sodium in a pure form has no electrons to gain, donate or share with another atom since it is in neutral state. Therefore, the oxidation number of sodium $(Na)$ in pure sodium, $Na$ is $0$.

Note:
Oxidation-reduction reaction is also known as redox reaction and can be defined as a type of chemical reaction that involves transfer of electrons between two atoms or species. If an atom gains electron from another atom, it is said to have been reduced; in the other case, when an atom loses electron, it is called to have been oxidized.