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Question

Question: The half life period of a radioactive substance is 5 min. The amount of substance decayed in 20 min ...

The half life period of a radioactive substance is 5 min. The amount of substance decayed in 20 min will be.

A

93.75%

B

75%

C

25%

D

6.25%

Answer

93.75%

Explanation

Solution

Number of half lives in 20 min = n =205=4= \frac{20}{5} = 4

Fraction of material remains after four half lives =116= \frac{1}{16}

Hence fraction that decays =1116=1516=93.75%= 1 - \frac{1}{16} = \frac{15}{16} = 93.75\%