Question

why niobium and tantalam have almost same radius​

Answer 1

Answer:

Due to lanthanide contraction. As the shielding of 4f orbitals are not particularly effective though there is increasing nuclear charge the elements immediately following the lanthanide have atomic radii similar.

Answer 2

Answer:

The reason is,

Due to lanthanide contraction. As the shielding of 4f orbitals are not particularly effective though there is increasing nuclear charge the elements immediately following the lanthanide have atomic radii similar.