The half-life of strontium-90 is about 29 years. How many half-lives have elapsed when 6.25% of O 1

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The question is incomplete, the complete question is;

The half-life of strontium-90 is about 29 years. How many half-lives have elapsed when 6.25% of a strontium- 90 sample remains in the container?

4 half lives

Explanation:

From;

N/No = (1/2)^t/t1/2

N= amount of strontium-90 present at time t

No= amount of strontium-90 originally present

t= time taken

t1/2 = half life of strontium-90

But N= 0.0625No

Hence;

0.0625No/No = (1/2)^t/29

0.0625 = (1/2)^t/29

(1/2)^4 = (1/2)^t/29

4 = t/29

t = 4 × 29

t= 116 years

Hence four half lives have elapsed

beta decay is the answer