Question

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

Answer 1

If `rho=2.8*g*L^-1`....

Explanation:

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. `Cl_2` is approx. `3*g*L^-1`, under normal conditions, so `Z=??` ....you need to re-specify the question...