Define 'activity' of a radioactive material and write its S.I.unit.
(ii) Plot a graph showing variation of activity of a given radioactive sample with time.
(iii) The sequence of stepwise decay of a radioactive nucleus is ` Doverset(alpha)to D_1overset(beta^1)to D_2`.
If the atomic number and mass number of `D_2` are 71 and 176 respectively, what are their corresponding values of D?