question_answer

Half-lives of two radioactive elements A and B are 20 minutes and 40 minutes, respectively. Initially, the samples have equal number of nuclei. After 80 minutes , the ratio of decayed numbers of A and B nuclei will be :-                                        [JEE MAIN - I 3-4-2016]

A) 5 : 4

B) 1 : 16

C) 4 : 1

D) 1 : 4

Correct Answer: A

Solution :

[a]

no. of nuclei of A decayed

no. of nuclei of B decayed

required ratio