Chemistry - Mole Concept Question with Solution | TestHub

The law of multiple proportions states that when two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in the ratio of small whole numbers.

For a pair of compounds to demonstrate this law, they must be composed of the exact same two elements.

$\mathrm{NO}$ and ${\mathrm{NO}}_2$ are composed of N and O.

$\mathrm{CO}$ and ${\mathrm{CO}}_2$ are composed of C and O.

${\mathrm{H}}_2\mathrm{O}$ and ${\mathrm{H}}_2{\mathrm{O}}_2$ are composed of H and O.

${\mathrm{Na}}_2\mathrm{S}$ and $\mathrm{NaF}$ are composed of three different elements: Na, S, and F. Therefore, they cannot demonstrate the law of multiple proportions.

Answer: ${\mathrm{Na}}_2\mathrm{S},\mathrm{NaF}$