A 0.199-gram sample of a pure gaseous compound occupies 122mL at 100OC and 790 torr. What is the molar mass of the compound? ( since you are using the ideal gas equation, do not forget to convert torr to atm C.F. 1atm = 760 torr)
Use PV = nRT
P = 790/760 = ?
V = 0.122 L
Not clear what T is. Could be 100 or could be 1000.
If that is T = 100 C then T = 273 + 100 = ?
R = 0.08205
Solve for n = moles.
Then mole = grams/molar mass. You know moles from above and grams. Solve for molar mass. Post your work if you get stuck.