Verified answer

I passed a mass of gas recently,

in my country we have the mass gas pass festival

i am judge of the most pungent aroma contest

Use the ideal gas law:

PV = nRT

685 torr*(1 atm/760 torr) = 0.901 atm

(0.901 atm)(.875L) = n(0.08206 L atm / K mol)(308 K)

n = 0.0312 moles

To get molar mass, divide mass by moles:

2.5g/0.0312 moles = 80.1 g/mol

Good luck!