Periodicity is best defined as: the fact that elements increase in atomic mass in a regular way. the repeating nature of physical and chemical properties with increasing atomic number. the regular growth of atomic size with atomic mass. the consistent decrease of nuclear charge with atomic mass. the repeating nature of atomic nuclear structure.

The elements present in nature or discovered so far are arranged in the form of a table known as periodic table. This creation of table was started with previous scientists like

i) Dobereiner's law of triads: according to it the atomic mass of middle element is average of atomic mass of side elements.

ii) Newland's law of octave: the properties of elements are repeated after seven elements.

iii) Mendleev's periodic table: it was a regular arrangement of by then discovered elements based on their atomic mass.

Now

We have periodic table known as long form or modern periodic table. This table is based on atomic number. According to it , there is periodicity in the physical and chemical properties of elements if they are arranged in certain groups and periods based on their atomic number.