What is the density of carbon dioxide at stp? 46.0 g/l 22.0 g/l 5.09 × 10-1 g/l 1.96 g/l?

Density (kg/m³) = mass (kg) / Volume (m³)
 d = m/V                 (1)

Ideal gas law,
PV = nRT               (2)

Where, P is the pressure of the gas (Pa), V is the volume of the gas (m³), n is the number of moles of gas (mol), R is the universal gas constant ( 8.314 J mol⁻¹ K⁻¹) and T is temperature in Kelvin.

n = m/M          (3)

Where, n is number of moles, m is mass and M is molar mass.

From (2) and (3),
PV = (m/M) RT

By rearranging,
P = (m/VM)RT              (4)

From (1) and (4)
P = (dRT) / M

P =  standard pressure = 1 atm = 101325 pa
d = ?
R = 8.314 J mol⁻¹ K⁻¹
T = Standard temperature = 273 K
M = 44 g/mol = 44 x 10⁻³ kg/mol

By substitution,
101325 Pa = (d x 8.314 J mol⁻¹ K⁻¹ x 273 K) / 44 x 10⁻³ kg/mol
               d = (101325 Pa x 44 x 10⁻³ kg/mol) / (8.314 J mol⁻¹ K⁻¹ x 273 K)
               d = 1.96 kg m⁻³ = 1.96 g/L

Hence, the density of the CO₂ at STP is 1.96 g/L

Assumption made is "CO₂ gas has an ideal gas behavior".

What? i don’t understand