chemical
posted by steve .
The vapor pressure of mercury at 77¢K is 0.0018 mmHg. The atomic weight of mercury is 200.6 g/mole. If the mercury vapor were allowed to reach equilibrium at this temperature in an enclosed space, what would be the mercury vapor concentration in the space?

The problem doesn't give a volume and that affects concn; however, I would use 1 L for V and use PV = nRT, solve for n and convert to grams. That will will you the concn in g/L.
Use PV = nRT