What is meant by periodicity? Why the properties of elements in the same group are similar?
Periodicity is the tendency of a property to recur at regular intervals in the modern periodic table.
In the modern periodic table, the elements are classified on the basis of the electronic configuration of the outermost orbits of the elements.
In a given group, the electronic configuration of the valence orbit of all elements is same. Thus, the elements in the same group show similar properties.