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?

Explanation

As mass number of each `alpha` particles is `4` units and its charge number is `2` units, therefore, for `D_(4)A=176-8=168 Z=71-4=67`
Now charge no. of `beta` is `-1` and its mass number is zero, therefore, for `D`
`A=176+0+4=180 Z=71-1+2=72`