You have 2.394 x 102 mL of oxygen gas (O2) at 7.20 x 102 mm of Hg and 78 oC.

What is the mass of the sample in milligrams?

We are given with

V = 2.394 x 102 mL

P = 7.20 x 102 mm of Hg

T = 78 oC

We are asked to determine the mass of the sample in milligrams

Using the ideal gas law

n = PV / RT

n = 7.20 x 102 mm of Hg (2.394 x 102 mL) / R (78 + 273)

Use the appropriate value for R or just convert the values to SI and use R = 8.314

Then, solve for the mass of the sample by using the MW Oxygen which is 16 g/mol