Answer :
The gas is most likely methane (CH₄)
Further explanation
In general, the gas equation can be written
[tex]\large{\boxed{\bold{PV=nRT}}}[/tex]
where
P = pressure, atm
V = volume, liter
n = number of moles
R = gas constant = 0.08205 l.atm / mol K
T = temperature, Kelvin
[tex]\tt PV=\dfrac{mass}{M}RT\\\\M=\dfrac{mRT}{PV}=\dfrac{0.817\times 0.082\times 300}{1,00658\times 1.25}=15.97\approx=16[/tex]
So the gas is most likely methane (CH₄ )