Question

Half life period of radium is $1600years$. $2gm$ of radium undergoes decay and gets reduced to $0.125gm$ in:

• A. $3200years$
• B. $25600years$
• C. $8000years$
• D. $6400years$

Answer 1

The correct option is D $6400years$

$t_{1/2}=1600yrs$

Fraction of radium left $=\frac{0.125}{2}$

$=\frac{1}{16}$

$=(\frac{1}{2}{)}^4$

i.e. The decay time is 4 half-lifes $=4\times 1600yrs$$=6400yrs$