1.

A radioactive isotope has a half-life of 10 days. If today 125 mg is left over, what was its original weight 40 days earlier

Answer»

2g
600 mg
1 g
1.5 g

Solution :`N = N_(0) ((1)/(2))^(n) .n = (40)/(10) = 4`
`(125)/(1000) = N_(0) ((1)/(2))^(4), N_(0) = (125)/(1000) xx 2 xx 2 xx 2 xx 2 = 2g`


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