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Given below are two statement : one is labelled as Assertion A and the other is labelled as Reason R. Assertion A : Size of Bk³⁺ ion is less than Np³⁺ ion. Reason R : The above is a consequence of the lanthanoid contraction. In the light of the above statements, choose the correct answer from the options given below :

1. A is false but R is true
2. Both A and R are true but R is not the correct explanation of A
3. Both A and R are true and R is the correct explanation of A
4. A is true but R is false

Correct answer: A is false but R is true

Solution

The assertion is incorrect because the size of Bk³⁺ is actually larger than Np³⁺ due to the effects of the actinide contraction, while the reason is true as the lanthanoid contraction does affect ionic sizes in the periodic table.

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