Question

Determine the molecular formula of phosphorus.

phosphorus gas has a density of 0.617 g/L at 70 and 200 Celsius ...

Answer 1

* at 790 torr not 70

Answer 2

70 what?
Use p*molar mass = density*R*T
Solve for molar mass, then
molar mass/30.97 = # P atoms/molecule.