The periodic trend in atomic radius ● As we go left to right across the period the size of the atom decrease. ● This is because the nuclear charge increases while moving from left to right. ● The nuclear charge attracts electrons and hence reduces the atomic radius (or atomic size). ● B, C, N, O belongs to the same period (IInd Period). ● We can see this in periodic table the arrangements of these atoms from left to right is B, C, N, O. So, B being at the leftmost among them has the highest atomic radius. B > C > N > O is the correct sequence.