Is the largest number of molecules in 36 g of water or 54 g of dinitrogen pentaoxide?
I'm stuck, because both of them are having two moles of each of the respective molecules.


Are you sure?

\begin{align}
M(\ce{H2O})  &amp;= \pu{18 g mol^-1} &amp;
\implies \pu{36 g} &amp;\mathop{\hat{=}} \pu{2 mol} \\
M(\ce{N2O5}) &amp;= \pu{108 g mol^-1} &amp;
\implies \pu{54 g} &amp;\mathop{\hat{=}} \pu{0.5 mol} \\
\end{align}