We’re being asked to rank 0.50 mol H2O, 23 g Na, 6.0x1023 N2 molecules in order of decreasing number of atoms without any detailed calculations.
We have to convert all of the given units of each sample into units of atom so that we can compare them.
For 0.50 mol H2O,
The flow of the calculation will be:
Moles H2O (Avogadro's number) → Molecules of H2O (number of atoms per molecule) → Atoms of H2O
Without doing any detailed calculations (but using a periodic table to give atomic weights), rank the following samples in order of decreasing number of atoms: 0.50 mol H2O, 23 g Na, 6.0 x 1023 N2 molecules.