A sample has $1.6\times 10^{20}$ atoms of a nuclide of half-life $8.0$ days. Use $\ln 2=0.693$ and $1\mathrm{day}=86400\mathrm{s}$. Which statements are correct?

1. AAbout $2.0\times 10^{19}$ atoms remain after $24$ days.
2. BThe initial activity is about $1.6\times 10^{14}\mathrm{dps}$.
3. CThe mean life is about $5.5$ days.
4. DAbout $1.2\times 10^{20}$ atoms decay in the first $16$ days.