Write the relation between mass number and atomic number.

Atomic number:

1. The atomic number of an element is equal to the number of protons in the nucleus of an atom.
2. The atomic number is denoted by $\mathrm{Z}$.

Mass number:

1. The mass number is defined as the sun of number of protons and number of neutrons in an atom.
2. The mass number is denoted by $\mathrm{A}$.

Relationship between atomic number and mass number:

Mass number$=$Number of protons$+$Number of neutrons

Now, Number of protons$=$Atomic number

Thus,

Mass number$=$Atomic number$+$Number of neutrons