Provide a possible explanation for why the atomic radii of Nb and Ta are almost the same even if they are on different periods in the periodic table.

• A. The 4f electrons in Ta do not effectively shield the outer electrons, pulling the electron closer to the nucleus hence a smaller atomic radius.
• B. Ta has more protons than Nb which cancels out the effect of additional electrons in Ta, hence a smaller atomic radius.
• C. The atomic radius of elements decreases as you go down a group.
• D. The 4f electrons do not significantly contribute to the overall size of the Ta atom, which caused Ta and Nb to have the same radii.

Answer: (A)