Answer:
The final volume of the gas is 36.1 L.
Explanation:
Given:
Initial pressure of the gas is, 
Final pressure of the gas is, 
Initial volume of the gas is, 
Final volume of the gas is, 
Here, we shall use Boyle's Law which states that for a process under constant temperature, the pressure of the gas changes inversely with the change in volume.
Here, the pressure is increased. So, the volume of the gas is decreased.
Therefore, as per Boyle's Law:

So, the final volume of the gas is 36.1 L.
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We can use the ideal gas law equation to find the number of moles in the gas
PV = nRTwhere P - pressure - 1.2 atm x 101 325 Pa/atm = 121 590 Pa
V - volume - 3.94 x 10⁻³ m³
n - number of moles
R - universal gas constant - 8.314 Jmol⁻¹K⁻¹
T - temperature - 15 °C + 273 = 288 K
substituting the values in the equation
121 590 Pa x 3.94 x 10⁻³ m³ = n x 8.314 Jmol⁻¹K⁻¹ x 288 K
n = 0.200 mol
molar mass of gas is = mass / number of moles
molar mass = 12.8 g / 0.200 mol = 64 g/mol
molar mass of gas is 64 g/mol
It would be polymer !!!!!