How is an atom represented using notation? Provide an example.

(N/A) An atom of an element $X$ is represented by placing the mass number $A$ as a left superscript and the atomic number $Z$ as a left subscript.
The notation is written as ${ }_{Z}^{A}X$.
Here,$X$ is the element symbol,$A$ is the mass number,and $Z$ is the atomic number.
Example: For sodium $(Na)$,the atomic number $(Z)$ is $11$ and the mass number $(A)$ is $23$.
Therefore,the notation is ${ }_{11}^{23}Na$.