Which sample contains the largest number of atoms?

$$\begin{gathered} 1 \mathrm{mg} {\mathrm{C}}_4{\mathrm{H}}_{10}=\frac{14\mathrm{N}}{58}\times {10}^{-3} \\ 1 \mathrm{mg} {\mathrm{N}}_2=\frac{2\mathrm{N}\times {10}^{-3}}{28} \\ 1 \mathrm{mg} \mathrm{Na}=\frac{\mathrm{N}\times {10}^{-3}}{23}\text{ atoms, } \\ 1 \mathrm{mL}=1{\mathrm{gH}}_2\mathrm{O}=\frac{3\mathrm{N}}{18}\text{ atoms } \end{gathered}$$

( $\because$Mg of a substance = N molecules = a x N atoms; where a is number of atoms in one molecule).