For which of the following parameters would the structural isomers ${\text{C}}_2{\text{H}}_5\text{OH}$ and ${\text{CH}}_3{\text{OCH}}_3$ be expected to have the same values? (Assume ideal behavior)

${\text{C}}_2{\text{H}}_5\text{OH}$ (ethanol) and ${\text{CH}}_3{\text{OCH}}_3$ (dimethyl ether) are structural isomers with the same molecular formula and thus the same molecular weight.
Density of a gas $d=\frac{PM}{RT}$.
At the same temperature ($T$) and pressure ($P$), since the molecular weights ($M$) are identical, their gaseous densities will be the same.
Other properties like boiling point, vapor pressure, and heat of vaporization depend on intermolecular forces (hydrogen bonding in ethanol vs. dipole-dipole in ether), which are different.