Question

The active amount of radioactive substance is left after one hour whose half life is 20 minutes is

Answer 1

125g if you take 1kg initially

Answer 2

The amount of the active amount of radioactive substance is left after one hour is $\frac{1}{8}$ of the original amount.

Explanation:

Formula used :

$a=\frac{a_o}{2^n}$

where,

a = amount of reactant left after n-half lives = ?

$a_o$ = let Initial amount of the reactant = 100 g

n = number of half lives= $\frac{\text {total time}}{\text {half life}}=\frac{60min}{20min}=3$

Putting values in above equation, we get:

$a=\frac{100}{2^3}$

$a=12.5g$

Therefore, the amount of the active amount of radioactive substance is left after one hour is $\frac{1}{8}$ of the original amount

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