which statement would be the most useful for deriving the ideal gas law?\nvolume is directly proportional to…

Answer:

Volume is directly proportional to the number of moles.

Brief Explanations:

The ideal - gas law is $PV = nRT$. From this, when $P$ and $T$ are constant, $V\propto n$. The other statements are incorrect according to the ideal - gas law. Volume is directly proportional to temperature ($V\propto T$ when $P$ and $n$ are constant), pressure is inversely proportional to volume ($P\propto\frac{1}{V}$ when $n$ and $T$ are constant), and pressure is directly proportional to the number of moles ($P\propto n$ when $V$ and $T$ are constant).