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Q.

Half life of longest lived radioactive isotope of Francium is

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a

21 hr

b

21 sec

c

21 min

d

12 min

answer is C.

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Detailed Solution

Among 1^st group elements, ‘Fr’ is radio active element.The longest lived isotope is ${}^{223}{Fr}$ having a half - life of 21 minutes.

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Half life of longest lived radioactive isotope of Francium is