Answer
$0.91g$
Work Step by Step
$\frac{\Delta N}{\Delta t}=\lambda N$
$\lambda=\frac{\ln(2)}{T_{0.5}}=1.75998\times10^{-17}s^{-1}$
$N=\frac{2.4\times10^5s^{-1}}{1.75998\times10^{-17}s^{-1}}=1.36365\times10^{22}$nuclei
$m=1.36365\times10^{22}nuclei\times\frac{1 a}{nucleus}\times\frac{1mol}{6.02\times10^{23}a}\times39.963998\frac{g}{mol}=0.91g$
