# How do we determine what substance has rho_"substance"=2.8*g*L^-1?

If $\rho = 2.8 \cdot g \cdot {L}^{-} 1$....
Is it an element, is it a compound? Given the context of the question, this is an elemental gas.... I happen to recall that the density of chlorine, i.e. $C {l}_{2}$ is approx. $3 \cdot g \cdot {L}^{-} 1$, under normal conditions, so Z=?? ....you need to re-specify the question...