Considering measurements rounded to the nearest pm, the atomic radii of Nb (146 pm) and Ta (146 pm) are practically identical. Explain this observation.

Due to the poor shielding of 6s electrons, the shielding effect is insufficient to counter the decrease in radius caused by increasing nuclear charge, allowing Ta to have an identical radius to Nb.

Due to the excessive shielding of 4f electrons, the shielding effect is insufficient to counter the decrease in radius caused by increasing nuclear charge, allowing Ta to have an identical radius to Nb.

Due to the poor shielding of 4f electrons, the shielding effect is insufficient to counter the decrease in radius caused by increasing nuclear charge, allowing Ta to have an identical radius to Nb.

Due to the excessive shielding of 6s electrons, the shielding effect is insufficient to counter the decrease in radius caused by increasing nuclear charge, allowing Ta to have an identical radius to Nb.