Question

Which is the lightest gas amongst `CO`, `CO_2`, `"chlorine"`, `CS`, `Xe`?

Answer 1

Got a Periodic Table? You simply have to add up the appropriate masses.

Explanation:

The one trick in this question is the molecular weight of chlorine gas. Save for the Noble Gases, ALL the elemental gases are bimolecular: `H_2`, `N_2`, `O_2`, `F_2`, `Cl_2` (in fact all the halogens are bimolecular in the elemental state, gas, solid, or liquid).

So I suspect the lightest gas will be carbon monoxide, and the heaviest gas xenon. But please make sure I am right!