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Question

A radioactive isotope, having a half life of 3 days was received after 9 days. It was found that there was only 4 gms of the isotope left in the container. The initial weight of the isotope, when it was packed, must be,

A
8 gms
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B
32 gms
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C
48 gms
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D
64 gms
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Solution

The correct option is B 32 gms
T=3 days, t=9 days, m=4 gms m0=?
We know that,
t=nT
9=n×3
n=3
i.e. the time elapsed is equal to three times the half life.

Now, m=m02n

4=m023
m0=4×8=32 gms

Hence, (B) is the correct answer.

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