At a given instant there are 25% undecayed rodioctive nuclei in sample After 10 s the number of undecyed nuclei reduces to 12.5 % calculate the mean life of the nuclei .

Explanation

thea number of undecayed nuclei reduces from 25% to 12.5% in 10 s . It means that the half -life of the sample is 10 s.
`i.e., T_(1//2)=10s`
`But T_(1//2)=0.0631//lamda , "where"lamda " is decay"`
`thus , lamda =(0.6931)/(T_(1//2))=(0.6931)/(10s)`
the mean life of the sample ,
`tau=1//lamda =(10)/(0.6931)=14.435s`