The correct order of radius is:-A Fe > Co > Ni B Li > Na > K C Ne > F > O D Ne > O > F

The correct order of atomic radii is determined by two factors: the number of energy levels and the effective nuclear charge.

A. Fe > Co > Ni This order is incorrect. As we move from left to right across a period in the periodic table, the atomic radius generally decreases. This is because electrons are being added to the same energy level while the nucleus is increasing in charge. The increase in nuclear charge attracts the electrons more strongly, pulling them closer to the nucleus.

B. Li > Na > K This order is incorrect. As we move down a group in the periodic table, the atomic radius generally increases. This is because electrons are being added to new energy levels that are further from the nucleus.

C. Ne > F > O This order is incorrect. As we move from left to right across a period in the periodic table, the atomic radius generally decreases. This is because electrons are being added to the same energy level while the nucleus is increasing in charge. The increase in nuclear charge attracts the electrons more strongly, pulling them closer to the nucleus.

D. Ne > O > F This order is correct. As we move from right to left across a period in the periodic table, the atomic radius generally increases. This is because the nuclear charge is decreasing while electrons are being removed from the same energy level. The decrease in nuclear charge attracts the electrons less strongly, allowing them to move further from the nucleus.