What is a periodic property? How the following properties vary in a group and in a period? Expain
(a) Atomic radius.

Explanation

Periodic property :Periodicity means that when elements are arranged accoding to their electronic configuratiin , the properties of elements in the perioodic table reoccr at regular intervals - such properties which reoccur are called called as periodic properties
change of properties in a group and a period :

Explanation :
a ) Atomic radius : the a group as we go down the atomic nuclear of the element is taken as atomic radius .
Variation in Group In group as we go down , the atomic nuuclear of the element increases , hence a new shell is added .As a result ,the distance between nucleus and the outer shell increases . This is the reason why the atomic radius increases as we go down in a group .
Variation in period : Atomic radii of element decreas acoss a period from left to right AS we go from left to right , electrons enter into the same than main shell or even inner shell . but nuclear charge increases , hence the nuclear attraction on the outer shell increaes .AS a result the size is the atom decreases .