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A radioactive isotope has a half-life of...

A radioactive isotope has a half-life of 8 days. If today 125 mg is left over. What was its original weight 32 days earlier ?

A

a) 6g

B

b) 5g

C

c) 4g

D

d) 2g

Text Solution

Verified by Experts

The correct Answer is:
D
`t _(1//2) = 8` days,` N = 125 mg, N _(0) = ?, T = 32 ` days.
`T = n xx t _(1//2)`
`32 = n xx 8`
`n = 4`
`N = _(0) ((1)/(2)) ^(n)`
`125 = N _(0) ((1)/(2)) ^(4)`
`125 = N _(0) xx (1)/(16)`
`N = 125 xx 16 = 200- mg = 2 g`
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