Explain the need for a reference atom for atomic mass. Give some information about two reference atoms.

Hint: Atomic mass is defined as the sum of the protons and the neutrons in the nucleus of an atom. Number of electrons present in an atom represents its atomic number. If there will be no reference atom to refer to for atomic mass, then the mass values will become more complex to memorize.

Complete step by step answer:
Now we will take an example of two references that we use on a daily basis in chemistry.
Hydrogen (atomic number= $1$)
We know that atomic number is equal to number of electrons present in an atom
Thus, number of electrons in Hydrogen will be =$1$
Number of Protons present in an atom of Hydrogen = $1$
But hydrogen do not has neutron in it
Thus, the atomic mass will be equal to number of protons and number of electrons=$1 + 0 = 1{\text{ }}$ amu approx., which is actually $1.673 \times {10^{^ - 27}}$ grams.
Carbon (atomic number= 6)
We know that atomic number is equal to number of electrons present in an atom
Thus, number of electrons in carbon will be =$6$
Protons present in an atom of carbon = $6$= number of neutrons
Thus, the atomic mass will be equal to the number of protons and number of electrons=$6 + 6 = 12{\text{ }}$ amu approx., which is actually $12.0107$ grams.
Now if we do not consider the relative mass, then the complex mass will become difficult to memorize.


Note:
The mass of an atom is measured in AMU, which is the Standard International (SI) unit of measurement defined as mass of an atom which is exactly equal to mass of one-twelfth of the carbon.