The activity of a freshly prepared radioactive sample is `10^(10)` disintegrations per second , whose mean life is `10^(9)s` The mass of an atom of this radioisotope is `10^(-25) kg ` The mass (in mg) of the radioactive sample is

Options

A. `1`
B. `2`
C. `3`
D. `4`

Answer

A

Explanation

Activity, `A=lambdaN=1/tauN [:' lambda=1/tau]`
Where `tau` is the mean life time of given sample.
`:. N=Atau=(10^(10)decays//sec)xx(10^(9)s)`
`=10^(19)"atoms"`
Mass of the sample, m=Nx(mass of one atom)
`=10^(19)xx10^(-25)kg=10^(-6)kg=1mg`