# Would equal volumes of two different substances have the same or different masses?

$\text{Density"="Mass"/"Volume}$, and $\rho$ is a characteristic property of all materials. Gases tend to be low density materials. Condensed phases, solids, and liquids, are high density materials.
According to this site, air at sea level, and at a temperature of $15$ ""^@C has $\rho = 1.225 \cdot k g \cdot {m}^{-} 3$.