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13.Nuclei
medium
The half-life of radium is about $1600$ years. Of $100\, g$ of radium existing now, $25\, g$ will remain unchanged after .......... $years$
A
$2400$
B
$3200$
C
$4800$
D
$6400$
(AIPMT-2004)
Solution
(b) $M = {M_0}{\left( {\frac{1}{2}} \right)^{\frac{t}{{{T_{1/2}}}}}}$
$ \Rightarrow 25 = 100{\left( {\frac{1}{2}} \right)^{\frac{t}{{1600}}}}$
==> $t= 3200$ years.
Standard 12
Physics