can someone help me with this physics question please?

Mass, m = 2.1212 g
Volume, V = 1.49 L = 1.49 × 10⁻³ m³
Absolute temperature, T = 273 K
Pressure, P = 810.6 kPa = 810600 N/m²
Gas constant, R = 8.314 J / (mol K)
Molar mass, M = ? g/mol

PV = nRT
PV = (m/M)RT

Molar mass, M
= mRT/PV
= 2.1212 × 8.314 × 273 / [810600 × (1.49 × 10⁻³)]
= 3.99
≈ 4

From the Periodic Table, the atomic mass of helium is 4.
The gas is helium.


OR :
Mass, m = 2.1212 g
Volume, V = 1.49 L
Absolute temperature, T = 273 K
Pressure, P = 810.6 kPa = 810.6/101 kPa
Gas constant, R = 0.082 atm L / (mol K)
Molar mass, M = ? g/mol

PV = nRT
PV = (m/M)RT

Molar mass, M
= mRT/PV
= 2.1212 × 0.0821× 273 / [(810.6/101) × 1.49]
= 3.97
≈ 4

From the Periodic Table, the atomic mass of helium is 4.
The gas is helium.

...
here's a variation of PV=nRT
m/V R T = M P
T = 273 K
P = 810.6 / 101.3 = 8.00 atm
so
2.1212/1.49 *(0.0821) (273) = M (8.00)
M = 3.99
the other hint was monatomic gas
so we are looking for a noble gas with at. mass of about 4
and that is helium

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Well, if it is a monatomic gas, it's going to be one of the noble gases.

810.6 kPa is 8 atmospheres. Let's let the gas expand so that the pressure fall to 1 atm.pressure. So the volume is going to increase to

1.49 * 8 = 11.9 L

Density = mass / volume = (2.1212 / 11.9) = 0.178 g/L at s.t.p.

That's going to be helium then.