Chemistry - Mole Concept Question with Solution | TestHub

Number of atoms can be calculated as the product of the number of moles of the substance, the number of atoms per molecule, and Avogadro's number ($N_A$).

For $18$ grams of water ($H_{2}O$):
Molar mass of $H_{2}O=18\text{ g/mol}$
Moles of $H_{2}O=\frac{18}{18}=1\text{ mol}$
Atoms per molecule = $3$
Total atoms = $1\times 3\times N_A=3N_A$

For $24$ grams of dioxygen ($O_2$):
Molar mass of $O_2=32\text{ g/mol}$
Moles of $O_2=\frac{24}{32}=0.75\text{ mol}$
Atoms per molecule = $2$
Total atoms = $0.75\times 2\times N_A=1.5N_A$

For $22$ grams of carbon dioxide ($C{O}_2$):
Molar mass of $C{O}_2=44\text{ g/mol}$
Moles of $C{O}_2=\frac{22}{44}=0.5\text{ mol}$
Atoms per molecule = $3$
Total atoms = $0.5\times 3\times N_A=1.5N_A$

For $16$ grams of methane ($C{H}_4$):
Molar mass of $C{H}_4=16\text{ g/mol}$
Moles of $C{H}_4=\frac{16}{16}=1\text{ mol}$
Atoms per molecule = $5$
Total atoms = $1\times 5\times N_A=5N_A$

Methane contains the maximum number of atoms.

Answer: $16$ grams of methane