IF 42g of an unknown gas occupies a volume of 125L at 0.3bar pressure and 300Ktemperature,then the gasX could be

The gas is nitrogen.
by using the Gas Law PV=nRT
the required data has been already given in the question, use it in given equation to get the answer.
P=0.3 bar=30000 Pa
T=300K
given mass=42g
volume=125L=0.125 cubic meter
R=8.314 kj/mol
n=given mass/molar mass
using the data in the eauation we will get the molar mass 28 which is og nitrogen.