The half life of radioactive sample undergoing α -decay is 1 . 4 × 10 17 s . If the number of nuclei in the…

Recall the formula of activity of a radioactive element in terms of decay constat, $R=\lambda \mathrm{N}$, and we know that the relation between decay constant and half-life is, $T=\frac{0.693}{\lambda }$$\Rightarrow R=\frac{0.693}{T}\times \mathrm{N}$$\Rightarrow R=\frac{0.693}{1.4\times {10}^{17}}\times 2\times {10}^{21}$$\Rightarrow R={10}^4 \mathrm{Bq}$.