Periodic Trend:
The Atomic radius of atoms generally decreases from left to right across a period
Group Trend:
The atomic radius of atoms generally increases from top to bottom within a group. As atomic number increases down a group, there is a increase in the positive nuclear charge, however the co-occurring increase in the number of orbitals wins out, increasing the atomic radius down a group in the periodic table
Answer :
The Atom with the greatest atomic radius is chlorine. Fluorine can be ruled out because it is in the same period as oxygen and further to the right down the period. Chlorine has the largest atomic size because it is farthest down the group of any of the above elements listed.