The half life of radioactive sample undergoing α -decay is 1 . 4 ×...

Recall the formula of activity of a radioactive element in terms of decay constat,& $R = \lambdaN$, and we know that the relation between decay constant and half-life is,~$T = \dfrac{0 . 693}{λ}⇒ R = \dfrac{0 . 693}{T} \times N⇒ R = \dfrac{0 . 693}{1 . 4 \times {10}^{17}} \times 2 \times {10}^{21}⇒ R = {10}^{4}Bq$.&