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Which of the two has an almost similar size

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An Intiative by Sri Chaitanya

${Ca}_{20} and {Ir}_{31}$

$_{22} Ti and_{40} Zr$

${Nb}_{41} and_{73} Ta$

$_{39} Y and_{57} La$

answer is B.

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Detailed Solution

The regular decrease in the atomic and ionic radii of lanthanoids with increasing in atomic number is known as Lanthanoid contraction.
Due to lanthanoid contraction 2nd and 3rd transition series are nearly same size.(Ex : Zr and Hf : Nb and Ta.....)

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