A. 8%
B. 5%
C. 3%
D. 1%

Correct Answer:

Option C = 3%

Explanation

After 5 half-lives, the fraction of any radio-active substance left = (1/2)5 = 1/32
Thus the percentage of the original nuclie = 1/32/1 x 100/1
assuming the original amount is unity percentage left
= 1/32 x 1400/1 = 3.12

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