The Brainliest Answer!
As you move from left to right in a period, the amount of protons increases which in turn increases the magnetic pulling on the electrons (protons are positive which attract negatively charged electrons) which contracts the molecule. Since all of the molecules in the same period have the same number of electron orbitals, they will gradually be smaller in atomic size.
1 5 1
In Periodic Table, elements are arranged in increasing order, this is a reason that why size of atoms increases as we move down the group.

hope it will help you..

pls mark as the best..
1 5 1