a. Ar
b. Ne
c. N2
d. O2
I need to know how to do it, not just the answer.
3 Answers

start with
PV = nRT
n = mass / mw
substitute and rearrange..
PV = (mass / mw) RT
mw = (mass / V) x RT/P
now.. since density = mass / volume..
mw = density x RT/P
mw = (1.21 g/L) x (0.08206 Latm/moleK) x (280.15K) / (0.987 atm) = 28.2 g/mole
and of the 4 choices, N2 has mw = 28.0 g/mole.. so… “C” is the correct answer

Calculate the moles of gas contained in 1 L at 7.0 C and 0.987 atm:
n = PV/RT
n = 0.987 x 1 / (0.082057 x 280.1 K)
n = 0.04295 mole
1.21 g / 0.04294 mole = 28.2 g/mole
ANSWER: N2 (28.0 g/mole)

PV = nRT where T is temp, R is the constant 0.08206 atm, P is pressure (atm suggested), V is volume and n is moles. Assume 1 mole, with 280K (273+7*C), with .987 atm at P. Find Volume.
From volume, take their molecular weights and divide by that L to get the answer. I wanna guess (didn’t do calc so don’t trust it fully) Neon.