How do you represent the nucleus using isotopic notation?

Hint: One should know the definition of the isotopes and how the isotopic notation is written to solve this question. The isotopes of a chemical element have a similar number of protons but they differ from each other by the mass number.

Complete step by step answer:
By the atomic structure of the chemical element we know that the atom contains a center nucleus. In the nucleus of the atom positively charged protons and the neutral charged neutrons are concentrated. The negatively charged electrons are moving around the nucleus in a circular orbit.
As we know that all atoms of a chemical element have the same number of protons, but the individual atoms may have different numbers of neutrons. These differing atoms are known as the isotopes. Isotopes are defined as the species of an atom which contains the same atomic number but differs in the mass number.
The mass number is calculated by adding the number of protons and the number of neutrons.
To write the symbol for an isotope, the atomic number is placed at the subscript and the mass number (protons plus neutrons) are placed at the superscript to the left of the atomic symbol.
Let’s take the example of chlorine atoms. The chlorine atom has two isotopes. The symbols for the two naturally occurring isotopes of chlorine are written as follows:${}_{17}^{35}Cl$ and ${}_{17}^{37}Cl$.
So by the mass number present in the isotope, the nucleus can be represented as it contains protons and neutrons.

Note: The isotopes of an atom can also be shown by writing the name of the chemical element followed by the mass number as the atomic number is always the same for the atom. For example, Chlorine-35 and chlorine-37.