The standard Temperature and Pressure of a gas are 273.15 K and 1 atm respectively.
Argon exists as a monoatomic atom and has a atomic mass of 39.04 g/mol.
If the gas is acting Ideally then, According to Ideal Gas Equation density is given as,
d = P M / R T ------- (1)
Where,
R = Gas Constant = 0.08206 atm.L.mol⁻¹.K⁻¹
Now,
Putting Values in eq. 1
d = (1.00 atm × 39.04 g/mol) ÷ (0.08206 atm.L.mol⁻¹.K⁻¹ × 273.15 K
density = 1.74 g/L
