Question

The activity of a freshly prepared radio-active sample is ${10}^{10}$ disintegrations per second, whose mean life is ${10}^{9}s$. The mass of an atom of this radio-isotope is ${10}^{-25}$ kg. The mass (in mg) of the radioactive sample is

• A. $1$
• B. $2$
• C. $3$
• D. $4$

Answer 1

Answer: (A)

$1$

$\frac{dN}{N}=\lambda N$
Therefore, $N={10}^{19}$ atoms
Mass of sample $={10}^{-25}\times {10}^{19}kg$$=1mg$