Chemistry Density Question (Any help appreciated, thanks!)?

P : pressure
V : volume
n : number of moles
R : gas constant
T : temperature
m : mass
M : molar mass
ρ : density

PV = nRT and n = m/M
Then, PV = (m/M)RT
Then, PM = ρRT
Hence, M/T = ρR/P
When ρ and P are constant, M/T = constant
Hence, M₁/T₁ = M₂/T₂

He : M₁ = 4.003 g/mol, T₁ = ? K
Ar : M₂ = 39.95 g/mol, T₂ = 273 K

M₁/T₁ = M₂/T₂
Temperature of He, T₁ = T₂ × (M₁/M₂) = 273 × (4.003/39.95) = 27.4 K


The answer : 27.4 K

The molecular weight of argon is about 10 times that of helium, so the absolute temperature would have to be about 1/10, to make the helium as dense as the argon. Answer: 27.4 K.