Question

how do atomic radii vary in a period and in a group how do you explain the variation

Answer 1

in a period when we go from left to right then the atomic size decrease and atomic radii also because effective nuclear charge increases and screening effect decrease
in a group when we go up to down then the atomic size and atomic radii both increase because effective nuclear charge decrease and screening effect increases

Answer 2

Answer:

U can see from the above photos

I hope these images will help u to understand the variations of atomic radii along a period and down the group....