Assertion :Ionic radii of Ta and Nb are same Reason: The lanthanide contraction cancels almost exactly the normal size increase on descending a group of transition elements

Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

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Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion

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Assertion is correct but Reason is incorrect

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Both Assertion and Reason are incorrect

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Solution

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
The elements following the lanthanides in the periodic table are influenced by the lanthanide contraction as lanthanide contraction cancels almost exactly the normal size increase on descending a group of transition elements. For example, the atomic radius of the metal Nb(a period-5 transition element) and that of Ta(the corresponding period-6 element) are very similar even though the number of electrons increases.

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