= Solution
For a pure sample, $N=(1000/239)N_A=2.520\times10^{24}$ <nuclei>. <radioactive activity> is $\mathcal A=\lambda N$ with $\lambda=\ln2/t_{1/2}$. Using a year of 365.25 days,
$$
t_{1/2}=7.612\times10^{11}\,\mathrm s,\qquad
\boxed{\mathcal A_0=2.29\times10^{12}\,\mathrm{Bq}\simeq2.3\,\mathrm{TBq}}.
$$
The <mass number> supplies the approximate <molar mass> in grams per mole. This is initial parent activity; no daughter activity or <isotope> mixture has been assumed.
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